Infrared Spectroscopic and Electronic Structure Investigations of Beryllium Halide Molecules, Cations, and Anions in Noble Gas Matrices

Article abstract of DOI:10.1021/acs.jpca.7b09454

Laser-ablated Be atoms, cations, and electrons were reacted with F₂, ClF, Cl₂, NF₃, CCl₄, CF₂Cl₂, HCl, DCl, and SiCl₄ diluted in noble gases. The major products were the dihalides BeF₂, BeClF, BeCl₂, and the hydride chloride HBeCl, whose identities were confirmed by comparison with previous evaporative work, deuterium substitution, and vibrational frequency calculations. The matrix-isolated fundamental frequency of the BeF molecule is higher, and the frequency of BeCl is lower, than that determined for the gas-phase molecules. The BeF⁺ and BeCl⁺ cations formed strong dipole-induced dipole complexes in solid Ne, Ar, Kr, and Xe with stepwise increase in computed noble gas dissociation energies. Going down the family NgBeF⁺ and NgBeCl⁺ series (Ng = Ne, Ar, Kr, Xe) the Mulliken charges q(Be) decrease, while q(Ng) increases, and the dipole moments decrease, which suggests covalent bonding in the xenon species. We find that the largest intramatrix shift is Ne to Ar which follows the largest factor increase for the Ng atomic polarizabilities. Extra electrons produce Cl^-, which reacts with HCl to form the stable HCl₂^- anion and possibly with BeCl₂ to give BeCl₃^-. A weak band observed in neon experiments with F₂ is probably due to BeF₃^-.

Full text of DOI:10.1021/acs.jpca.7b09454

Article
pubs.acs.org/JPCA
Cite This: J. Phys. Chem. A XXXX, XXX, XXX-XXX
Infrared Spectroscopic and Electronic Structure Investigations of
Beryllium Halide Molecules, Cations, and Anions in Noble Gas
Matrices
Published as part of The Journal of Physical Chemistry virtual special issue “W. Lester S. Andrews Festschrift”.
Wenjie Yu,† Lester Andrews,*,‡ and Xuefeng Wang*,†,‡
†School of Chemical Science and Engineering, Tongji University, Shanghai 200092, China
‡Department of Chemistry, University of Virginia, Charlottesville, Virginia 22904-4319, United States
S
* Supporting Information
ABSTRACT: Laser-ablated Be atoms, cations, and electrons were reacted with F2, ClF,
Cl2, NF3, CCl4, CF2Cl2, HCl, DCl, and SiCl4 diluted in noble gases. The major
products were the dihalides BeF2, BeClF, BeCl2, and the hydride chloride HBeCl,
whose identities were confirmed by comparison with previous evaporative work,
deuterium substitution, and vibrational frequency calculations. The matrix-isolated
fundamental frequency of the BeF molecule is higher, and the frequency of BeCl is
lower, than that determined for the gas-phase molecules. The BeF+ and BeCl+ cations
formed strong dipole-induced dipole complexes in solid Ne, Ar, Kr, and Xe with
stepwise increase in computed noble gas dissociation energies. Going down the family
NgBeF+ and NgBeCl+ series (Ng = Ne, Ar, Kr, Xe) the Mulliken charges q(Be)
decrease, while q(Ng) increases, and the dipole moments decrease, which suggests covalent bonding in the xenon species. We
find that the largest intramatrix shift is Ne to Ar which follows the largest factor increase for the Ng atomic polarizabilities. Extra
electrons produce Cl−, which reacts with HCl to form the stable HCl2 anion and possibly with BeCl2 to give BeCl3 . A weak
−
−
−
band observed in neon experiments with F2 is probably due to BeF3 .
Veldkamp and Frenking computed these noble gas complexes
to be bound by 6.7, 9.3, and 12.6 kcal/mol, respectively.11
Following this special behavior for beryllium with an
electronegative partner, we decided to investigate beryllium
halides. The BeF2 and BeCl2 molecules have been observed in
noble gas matrices12 and in the gas phase,13 and the frequencies
of the monohalides are known from gas-phase electronic
spectra.9 We find that BeF2 has antisymmetric stretching
frequencies in solid neon and argon that are 26 and 9 cm−1
above the gas-phase value (1520 cm−1) and that the BeF
diatomic molecule fundamental in solid Ne, Ar, and Kr is 13.0,
5.6, and 0.5 cm−1 higher than the gas-phase mode (1229.2
cm−1).9 The chlorine counterparts exhibit similar behavior: the
BeCl2 absorption is 12 cm−1 above (in neon) and 1 cm−1 below
(in argon) the gas-phase measurement (1113 cm−1), and BeCl
is 4.2, 19.0, and 25.0 cm−1 below (in Ar, Kr, Xe) the gas-phase
mode (837.0 cm−1). These comparisons show that the matrix-
isolated Nen-BeF, Arn-BeF, and Krn-BeF dipole-induced dipole
complexes are stronger than the chlorine counterparts, and the
possibility of cation complexes must also be considered.
Pulsed laser ablation is known to produce metal cations from
mass spectroscopy and ion cyclotron resonance investiga-
INTRODUCTION
■
One of our earliest laser ablation targets for matrix infrared
investigations was boron, which upon condensation with
oxygen/argon samples, provided a number of new boron
oxides.1 Boron is difficult to evaporate because of container
problems with the liquid, but this is avoided by focused pulsed
laser ablation of a small amount of material, mostly atoms, from
a solid target. Since Be forms toxic compounds such a method,
which presents a trace amount of atoms for reaction, is desired.
Accordingly we have reacted laser ablated Be atoms with small
molecules such as O2, CO2, H2, CO, HCN, and C2H2.2−8 Of
most interest here is our discovery of the Ar-BeO complex2,3
and the simplest triatomic molecule BeH2.5 The most
interesting property of BeO in an argon matrix is that the
observed frequency, 1526.1 cm−1, is higher than the gas-phase
diatomic molecule frequency9 by 62.4 cm−1, and the oxygen
16/18 frequency ratio 1.0190 is slightly lower than the
calculated anharmonic ratio 1.0207 for the diatomic BeO
molecule.2 Ionic diatomic molecules typically exhibit large red
shifts when trapped in an argon matrix, for example, the major
absorption for the isoelectronic molecule LiF in solid argon is
at 838 cm−1, which is 56.5 cm−1 lower than the gas-phase
fundamental frequency (894.5 cm−1).9,10 From this comparison
Thompson and Andrews concluded that Ar-BeO forms a
bound dipole-induced dipole complex: additional experiments
using Kr and Xe formed even stronger complexes with BeO.2,3
Received: September 23, 2017
Revised: November 1, 2017
Published: November 1, 2017
© XXXX American Chemical Society
A
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tions.14,15 Accordingly, an extensive array of transition-metal
carbonyl cations, neutrals, and anions has been observed in
argon and neon matrixes based on 13C and 18O substitution in
the infrared spectra, the effect of adding the electron-trapping
CCl4 molecule to increase the infrared intensity of cation
absorptions and decrease the intensity of anion products, and
agreement with density functional frequency calculations.16−19
In addition the laser ablation plume contains high-energy UV
radiation, which can photoionize the metal atoms during the
matrix condensation process.20 In the following paper we
report the BeF+ and BeCl+ cations in matrices and find that the
calculated values for the Be−X stretching modes of Ne-BeF+
and Ne-BeCl+ are 15 and 61 cm−1 higher than the computed
values for the isolated diatomic cations, and the calculated
dissociation values for Ne from these complexes are 12 and 11
kcal/mol. We are not aware of gas-phase optical spectra of
these cations. The new molecules HBeCl and FBeCl were also
identified by matrix infrared spectra and theoretical frequency
calculations.
complex, and it is corrected for the basis set superposition error
(BSSE) using the full counterpoise method of Boys and
Bernardi.31 Localized orbital locator (LOL) and the non-
covalent interaction index (NCI)32 was introduced to
investigate the matrix interaction performed with the Multiwfn
program33 and visualized using the VMD package.34
RESULTS AND DISCUSSION
■
Laser-ablated beryllium atoms, cations, and electrons were
codeposited with F2, NF3, ClF, Cl2, CF2Cl2, CCl4, and SiCl4
diluted in noble gases, and the observations were compared
with previous work and density functional calculations of
energies, structures, and harmonic vibrational frequencies.
Infrared Spectra of Beryllium Fluorides. Figure 1
illustrates the neon matrix spectra of 1% F2 reacted with
EXPERIMENTAL AND COMPUTATIONAL
METHODS
■
Laser-ablated beryllium atoms and cations produced by
Nd:YAG laser (Continuum Minilite II) evaporation from the
solid (Johnson-Matthey, lump, 99.5%) were codeposited with
dilute mixtures (0.1−3.0%) of reagent gas (F2, ClF, Cl2, NF3,
CF2Cl2, CCl4, and SiCl4 from Air Products and Chemicals,
Ozark-Mahoning, Matheson, Air Products and Chemicals,
Yonghe Refrigerant, Sinopharm Chemical Reagent, Alfa
Aesar, respectively) in neon, argon, krypton or xenon (Spectra
Gases). The fluorine-bearing manifold was thoroughly
passivated with F2 before use, and this manifold was treated
with 150 torr of ClF overnight before use. Matrix/reagent
samples were codeposited onto a CsI window cooled to 4 K
using a closed-cycle refrigerator (Sumitomo): the window was
heated to 17 1 K for krypton at Virginia. These methods have
been described in detail elsewhere.7,16,20,21 After deposition,
infrared spectra were recorded at a resolution of 0.5 cm−1 and
accuracy of 0.1 cm−1 using a Nicolet iS50 spectrometer (in
Virginia) with MCT-A (4000 to 640 cm−1) and DTGS-KBr
(4000 to 540 cm−1) detectors or a Bruker Vertex 80v (in
Shanghai) with an MCT-B (4000 to 440 cm−1) detector.
Matrix samples were warmed and recooled (annealed, gold/
cobalt vs chromel thermocouple temperature measurement),
and more spectra were recorded. The samples were irradiated
by a mercury arc street lamp (Sylvania, 175 W, outer globe
removed, λ > 220 nm) for 10 min periods, and more spectra
were recorded. Additional annealings were performed, and final
spectra were recorded.
Theoretical calculations for possible reaction products were
performed with the Gaussian 09 package.22 In all instances, the
B3LYP hybrid density functional23,24 was used, and Be, F, Cl,
Ne, Ar, Kr, and hydrogen atoms employed the large 6-311+
+G(3df,3pd) Gaussian basis25 and cc-pVTZ basis,26 but the
heavier Xe atom required the SDD27 or cc-pVTZ-PP26
pseudopotential and basis set. Such density functional theory
(DFT) calculations predict vibrational frequencies with
reasonable accuracy for metal compounds.4,7,16,20,28,29 Geo-
metries were fully relaxed during optimization, and the
optimized geometries were confirmed by vibrational analysis.
Separate calculations with CCSD(T)30 were employed to
supplement the B3LYP results. The zero-point energy is
included in the calculation of binding energy for a metal
Figure 1. Infrared spectra in the product absorption regions for laser-
ablated Be atoms and cations codeposited with F2 in excess neon at 4
K: (a) Be + 1.0% F2 in Ne codeposited for 50 min. (b) After photolysis
with λ > 220 nm for 10 min, (c) after annealing to 8 K, and (d) after
annealing to 10 K.
laser-ablated beryllium atoms, which is dominated by a very
strong 1546.5 cm−1 absorption for BeF2 that is in agreement
with Snelson’s neon matrix measurement of a strong band
labeled 1545 in the published spectrum using a prism
instrument, but 1542 cm−1 was listed in the table of
frequencies.12 That early work codeposited thermally evapo-
rated molecules from the solid at high temperature (600−1000
°C) with neon onto a window at 4 K and made frequency
measurements with a prism spectrometer, which is not as
accurate as current Fourier transform IR instruments. Figure 1
also shows common fluorine impurity bands for CF4 at 1277.7
and OCF2 at 1237.5 cm−1 and the growth of absorption at
1490−1500 cm−1 on annealing, which arises from the OOF
radical owing to O2 impurity in the fluorine sample.35 A weak
new band labeled BeF was observed at 1241.6 cm−1 with a
slightly higher frequency shoulder: this feature is higher than
the gas-phase 1229.2 cm−1 frequency for BeF.9 Product
absorptions are listed in Table 1. Irradiation of the sample
with the full light of the mercury arc (λ > 220 nm) for 10 min
increased the BeF2 feature by 40%, while BeF decreased by
∼10%. Annealing the sample to 8 K almost doubled the latter
band and decreased the former band by ∼20%: the final
annealing to 10 K slightly decreased both features. Annealing
also increased a weak band at 1252 cm−1 in Figure 1d, which
can be assigned to (BeF2)2 based on additional work of
Snelson.36 Two additional neon matrix experiments gave
similar product absorptions.
Nitrogen trifluoride is also a good fluorine atom source, and
Figure 2 shows the reaction of Be with a 0.5% sample in neon.
The first spectrum is a predeposition of 5% of our sample
B
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Table 1. Infrared Absorptions for Beryllium Halide
Molecules from Reactions with Halogen Molecules in Noble
Gas Matrixes
molecules
neon
1546.5
argon
1529.4
krypton
BeF2
1525.8, 1541.6
1229.7
BeF
BeF+
Be35Cl2
Be35,37Cl2
Be37Cl2
BeCl
1242.2, 1241.6
1457.8
1234.8
1445.0
1111.6
1109.9
1108.2
818.8
1449.1, 1445.0
1102.7
1125.2
1123.5
1101.1
1121.8
1099.3
BeCl+
BeClF
1001.4
996.4, 994.8
1375.6
989.8
1391.9
1371.3
−
BeF3
1061.4 (tentative)
Figure 3. Infrared spectra in the product absorption regions for laser-
ablated Be atoms and cations codeposited with F2 in excess argon at 4
K: (a) Be + 2.0% F2 in Ar codeposited for 50 min. (b) After and
annealing to 20 K, (c) after photolysis with λ > 220 nm for 10 min, (d)
after and annealing to 25 K, and (e) after annealing to 30 K.
solid argon, and the weak band at 1246.3 cm−1, which also
increased on photolysis, is in agreement with that reported for
(BeF2)2.12,36 Another argon matrix experiment reproduced
these argon matrix observations.
The following experiment was done with Be and 1% F2 and
1% Kr in excess argon: the 1529.4 and 1489.2 cm−1 bands were
not shifted, but the other two product bands were red-shifted
slightly to 1444.7 and 1234.1 cm−1, which suggests a more
intimate involvement with the noble gas environment for the
latter two absorbing species labeled BeF+ and BeF.
The corresponding spectrum with Be and NF3 (1%) in argon
(not shown) produced the same bands as did the F2 reaction
with relatively more of the lower BeF band than the higher
BeF2 band, which was observed more clearly with only a trace
of the OCF2 absorptions. The upper band increased, and the
latter band decreased on photolysis as before. The 1445.0 cm−1
band was weaker than with the F2 reagent, but it behaved the
same on photolysis and annealing.
Figure 2. Infrared spectra in the product absorption regions for laser-
ablated Be atoms and cations codeposited with NF3 in excess neon at 4
K: (a) predeposition of 0.5% NF3 in Ne for 10 min, (b) same sample
codeposited with Be for 50 min, (c) after annealing to 8 K, and (d)
after photolysis with λ > 220 nm for 10 min.
without Be: in this region two NF3 bands were observed at
1540.4 and 1519.3 cm−1, and CF4 and OCF2 were again
observed. The BeF2 band at 1546.5 cm−1 was approximately the
same intensity (0.06 absorbance units) as in the reaction with
F2, and the BeF feature appeared at 1242.2 cm−1 with a lower-
frequency shoulder. The NF and NF2 photolysis products were
observed at 1119.8 and 936.1 cm−1, which shows that F atoms
are produced for reaction partners.9,35 Full arc photolysis
increased the BeF2 band by 30% and almost destroyed the BeF
peak.
Beryllium atoms were also reacted with 2% F2 in a krypton
matrix deposited at 17 1 K, and the spectra are shown in
Figure 4: it is anticipated that a significant proportion of our
fluorine will react with krypton under UV light from the
The corresponding spectrum with Be and F2 (2%) in argon is
illustrated in Figure 3. Codeposition for 50 min with Be
produced a strong sharp new band at 1529.4 cm−1, a weaker
band at 1445.0 cm−1, and a new feature at 1234.8 cm−1 below
the OCF2 peak. Notice that the OOF radical is observed at
1489.8 cm−1 from the reaction of F atoms with O2 impurity in
the fluorine,35 and this absorption increased on annealing,
decreased on photolysis, and provided more evidence for F
atom reactions in the matrix. Sample annealing to 20 K
increased the two higher bands and slightly decreased the lower
product band. Sample irradiation doubled the two upper bands,
decreased the lower band, produced a weaker satellite at 1233.8
cm−1, and increased another band labeled Be2F4 at 1246.3 cm−1
threefold. Sample annealing to 25 K decreased the strong BeF2
band, increased the 1445.0 cm−1 feature, and markedly
decreased the BeF band. Final annealing to 30 K decreased
all of the product absorptions. The highest band at 1529.4 cm−1
is close to the 1528 cm−1 assignment of Snelson to BeF2 in
Figure 4. Infrared spectra in the product absorption regions for laser-
ablated Be atoms and cations codeposited with F2 in excess krypton at
17 1 K: (a) Be + 2.0% F2 in Ar codeposited for 50 min. (b) After
photolysis with λ > 220 nm for 10 min both recorded using the
DTGS-KBr detector, (c) spectrum scanned again using the MCT-A
detector. (d) MCT-A spectrum after annealing to 30 K, (e) same after
annealing to 40 K.
C
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ablation plume.20,37 The first two spectra were recorded using
the DTGS-KBr detector, which enabled scans to lower
frequency with much less sensitivity. The first scan for
deposition shows a weak 578.4 cm−1 band37 for KrF2 along
with OOF (1487.9 cm−1), CF4 (1271.6 cm−1), and OCF2
(1235.0 cm−1) impurities.35 New product bands for BeF2 were
observed at 1525.8 and 1541.6 cm−1, which may be compared
with Snelson’s bands at 1524 and 1540 cm−1.12 In addition a
weak feature was observed at 1229.7 cm−1 labeled BeF just
below the OCF2 absorption. Photolysis with the full light of the
mercury arc doubled the BeF2 bands and substantially reduced
the BeF band as before, and it increased the KrF2 absorption by
an order of magnitude (Figure 4b). The higher region was
scanned again using the more sensitive MCT-A detector
(Figure 4c), and virtually the same spectrum was observed
along with a weak sharp band at 1449.1 cm−1. Annealing cycles
to 30 and 40 K decreased the product absorptions.
For the reaction with ClF in krypton BeClF is the strongest
product band at 1371.3 cm−1 followed by BeCl2 at 1102.3
cm−1: BeF2 was apparently not formed in Kr by diffusing F
atoms, reactions 3 and 4 in sequence, due to the favored
reaction to make KrF2. However, bimolecular reaction 1 with
Be and F2 to form BeF2 can compete with the Kr + F2 reaction
(Figure 4). Therefore, the primary reaction is Be insertion into
the halogen molecule to make the dihalide product molecules,
which are relaxed and trapped in the matrices. These are all
exothermic reactions 1, and they can proceed on sample
deposition and on UV photolysis. Some of the [BeX2]*
decomposes to BeX + X, reaction 2. The energy changes for
reactions 1, 2, 3, and 4 with F2 are negative 272, 106, 140, and
166 kcal/mol using B3LYP/6-311++G(3df,3pd). Laser-ablation
plume photolysis can, of course, photodissociate the halogen
molecules, and the Be addition reactions 3 and 4 can occur
particularly during the annealing process with solid neon and
argon. The energies for reaction 1 using the ClF and Cl2
reagents are negative 206 and 168 kcal/mol. Both CCl4 and
SiCl4 serve as Cl atom sources for laser-ablated Be by direct
reactions 5 and 5′) and through laser-plume photolysis.
Infrared Spectra of Beryllium Chloride Fluoride.
Reactions were done with ClF to synthesize BeClF and to
explore the reaction mechanism. Figure 5 compares reactions
Be + X2 → [BeX2]* → BeX2
(1)
Be + X2 → [BeX2]* → BeX + X
(2)
Be + X → [BeX]* → BeX
(3)
BeX + X → [BeX2]* → BeX2
(4)
Be + CCl4 → [BeCCl4]* ↔ BeCl + CCl3
(5)
Be + SiCl4 → [BeSiCl4]* → BeCl + SiCl3
(5′)
We also observe from the argon ClF experiment (Figure 5) that
BeClF increases the most on UV photolysis, reaction 1′, and
that BeF2 is much more intense than BeCl2, which suggests that
reaction 2′ favors the more exothermic formation of BeF over
BeCl. The computed energies for reaction 2′ and 2″ are
negative 81 and 36 kcal/mol, respectively (B3LYP/6-311+
+G(3df,3pd)). In addition F atoms from photodissociation of
ClF by the laser-ablation plume20 will diffuse more readily
through the argon matrix on annealing than will Cl atoms, so
reactions 3′ and 4′ are more likely to proceed with F than with
Cl atoms.
Figure 5. Infrared spectra in the product absorption regions for laser-
ablated Be atoms and cations codeposited with ClF and Cl2 + F2 in
excess argon at 4 K: (a) Be + 2.0% ClF in Ar codeposited for 50 min,
(b) after annealing to 25 K, (c) after photolysis with λ > 220 nm for 10
min, (d) Be + 1% F2 + 1% Cl2 in Ar codeposited for 50 min, (e) after
annealing to 25 K, and (f) after photolysis with λ > 220 nm for 10 min.
with ClF 2% in argon (a,b,c) and with 1% F2 and 1% Cl2 in
argon (d,e,f). The strong Cl isotopic doublet observed for ClF
at 767.7, 760.5 cm−1 is not shown. The first thing to notice is
the sharp new band labeled BeClF at 1375.6 cm−1, which
increases slightly on annealing to 25 K without much change in
the 1529.4 cm−1 band of BeF2 and the 1111.6, 1109.9 cm−1
doublet labeled BeCl2. Full arc photolysis increased the BeFCl
band by 50% and the other two dihalides by 20%. In contrast
the reaction with F2/Cl2 produced less BeFCl and more BeF2
and BeCl2, and the latter two species almost double on
photolysis, while the former increases only 60%. The BeF band
is again observed at 1234.8 cm−1, and it decreased on annealing
and photolysis as before.
Be + ClF → [BeClF]* → BeClF
Be + ClF → [BeClF]* → BeF + Cl
Be + ClF → [BeClF]* → BeCl + F
Be + F → [BeF]* → BeF
(1′)
(2′)
(2″)
(3′)
(4′)
BeF + F → [BeF ]* → BeF
2
2
Reactions were also done with CCl2F2 in an argon matrix
(Figure S2), and BeClF, BeF2, BeF, BeCl2, and BeCl were
observed. Notice such reactions gave less BeF2 and BeF than
BeCl2 and BeCl, since the C−F bond from CCl2F2 is harder to
cleave than the C−Cl bond during laser ablation.
Infrared Spectra of Beryllium Chlorides. Experiments
were performed for Be and Cl2 in the Ne, Ar, and Kr matrices,
and the major product band in each case was a resolved
chlorine isotopic triplet, which is shown in Figure 6 for all
three, and the peaks are listed in Table 1. A weak higher-
frequency peak in the neon and argon matrixes is probably due
With neon the ClF molecule has a resolved 35ClF and 37ClF
isotopic doublet at 771.6, 764.3 cm−1. Spectra for the reactions
of Be and ClF in a neon matrix are provided in Figure S1. In
neon the BeF2 band at 1546.5 cm−1 is the strongest product
followed by BeFCl at 1391.9 cm−1 and BeCl2 at 1125.2, 1123.6
cm−1. It is typical for neon matrix frequencies to be higher and
closer to gas-phase frequencies than argon matrix frequencies as
described in a noteworthy paper by Jacox.38 The gas-phase
fundamental for 35ClF is 773.83 cm−1.9
D
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involving Be atom reactions with the chlorine-bearing reagents
CCl4 and SiCl4.
Figure 7 compares spectra for Be atom reactions with CCl4
and SiCl4 in excess neon as sources for Cl atoms, and the major
product frequencies are listed in Table 2. Notice the bands
Table 2. Observed Vibrational Frequencies (cm−1) of Major
CCl4 and SiCl4 Reaction Products in Matrixes
molecules
BeCl2
neon
argon
krypton
xenon
1125.3
1123.6
1121.9
832.8
1111.5
1109.8
1108.3
817.7
813.4
2117.6
800.4
795.6
515.6
1613.1
768.6
763.7
995.9
993.0
705.6
1102.5
1101.1
1099.1
812.0
807.4
2111.4
795.0
790.2
508.7
1607.1
764.2
759.5
1096.1
BeCl
811.5
806.3
2108.5
790.7
785.9
500.2
828.2
HBeCl
811.8
806.8
Figure 6. Infrared spectra in the Be−Cl stretching region for laser-
ablated Be atoms and cations codeposited with Cl2 in excess neon,
argon, and krypton: (a) Be + 1.0% Cl2 in Ne codeposited for 50 min at
4 K. (b) After photolysis with λ > 220 nm for 10 min, (c) after
annealing to 10 K; (d) Be + 2.0% Cl2 in Ar codeposited for 50 min at 4
K. (e) After photolysis with λ > 220 nm for 10 min, (f) after annealing
to 25 K; (g) Be + 3.0% Cl2 in Kr codeposited for 50 min at 17 K. (h)
After annealing to 35 K, (i) after photolysis with λ > 220 nm for 10
min.
DBeCl
BeCl+
775.7
770.8
1001.7
998.3
710.8
760.5
755.7
−
BeCl3 (tentative)
688.9
663
686.5
678.8
644
−
HCl2
738
696
to a matrix site splitting. The broad band at 1116 cm−1 in the
neon sample is probably due to BeCl2 complexed with Cl2
reagent, as isolation is more difficult to achieve in the lower-
freezing neon matrix. A weak 818.8 cm−1 band is observed to
track with the strong isotopic triplet for BeCl2 in argon, and it is
assigned to BeCl based on agreement with the following work
common to both experiments: the strongest such product
absorption is the triplet of bands starting at 1125.3 cm−1 and
labeled BeCl2, which are within 0.1 cm−1 of the triplet
components observed from the Be reaction with chlorine in
Figure 6. Next a doublet of bands is observed at 832.8 and
828.2 cm−1, which is labeled BeCl. This band is very close to
Figure 7. Infrared spectra in the product absorption regions for laser-ablated Be atoms and cations codeposited with SiCl4 or CCl4 in excess neon at
4 K: (a) Be + 0.1% SiCl4 in Ne codeposited for 50 min, (b) after annealing to 10 K, (c) after photolysis with λ > 220 nm for 10 min, (d) after
annealing to 12 K; (e) Be + 0.1% CCl4 in Ne codeposited for 50 min, (f) after annealing to 10 K, (g) after photolysis with λ > 220 nm for 10 min,
(h) after annealing to 12 K.
E
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Table 3. Calculated Vibrational Frequencies (cm−1) and Intensities (km/mol, in Parentheses) of Major Products
B3LYP/6-311++g(3df,3pd)
35,37-Cl
B3LYP/cc-pVTZ
35,37-Cl
CCSD(T)/cc-pVTZ
35-Cl
37-Cl
35-Cl
37-Cl
35-Cl
35,37-Cl
37-Cl
BeCl2
1133.2(438)
400.4(0)
1131.4(437)
395.0(0)
1129.7(436)
389.5(0)
1133.3(424)
399.4(0)
1131.5(422)
394.0(0)
1129.8(421)
388.5(0)
1144.5
402.1
235.2
841.6
2187.3
822.8
511.8
1652.7
778.8
406.2
1007.0
1419.9
524.3
284.8
1142.7
396.6
234.9
1140.9
391.1
234.5
836.9
2187.2
817.8
511.6
1652.6
773.8
406.0
1001.4
1419.2
518.2
284.5
246.7(45 × 2)
835.7(126)
2210.6(162)
820.8(84)
246.3(45 × 2)
245.9(45 × 2)
831.1(125)
2210.6(162)
815.9(83)
241.3(45 × 2)
832.3(122)
2204.7(161)
819.5(82)
240.9(45 × 2)
240.5(45 × 2)
827.7(121)
2204.7(161)
814.6(81)
BeCl
HBeCl
525.2(168 × 2)
1669.3(141)
777.5(65)
525.1(168 × 2)
1669.1(141)
772.5(64)
520.4(165 × 2)
1665.4(140)
776.0(62)
520.3(165 × 2)
1665.2(140)
771.0(62)
DBeCl
417.3(109 × 2)
1014.7(201)
1399.8(403)
521.2(5)
417.1(108 × 2)
1009.1(202)
1399.2(402)
515.2(5)
413.4(107 × 2)
1009.5(200)
1411.5(383)
520.7(6)
413.2(107 × 2)
1003.9(200)
1410.8(382)
514.7(5)
BeCl+
FBeCl
291.3(89 × 2)
291.0(89 × 2)
289.4(87 × 2)
289.1(87 × 2)
BeF2
1565.0(381)
725.1(0)
1576.5(355)
726.3(0)
1584.2
726.9
330.6(156 × 2)
1249.1(118)
1457.7(255)
339.0(150 × 2)
1257.0(111)
1452.6(252)
333.4
BeF
BeF+
1260.5
1445.8
Figure 8. Infrared spectra in the product absorption regions for laser-ablated Be atoms and cations codeposited with SiCl4 or CCl4 in excess argon at
4 K: (a) Be + 0.1% SiCl4 in Ar codeposited for 60 min, (b) after annealing to 25 K, (c) after photolysis with λ > 220 nm for 10 min, (d) after
annealing to 35 K; (e) Be + 0.1% CCl4 in Ar codeposited for 60 min, (f) after annealing to 25 K, (g) after photolysis with λ > 220 nm for 10 min, (h)
after annealing to 35 K.
the 828.9 cm−1 fundamental frequency for BeCl in the gas
phase9 and to the computed values for BeCl in Table 3. In the
SiCl4 experiment HCl was observed at 2899.8 cm−1 and BeH at
1986.9 cm−1 (not shown); a doublet of bands at 811.8 and
806.8 cm−1 is labeled HBeCl, and the case for its identification
will be made as further observations are considered. We believe
that HCl arises from reaction of SiCl4 with trace water impurity
during sample preparation: HCl is not observed with CCl4. A
feature at 1001.7 cm−1 is marked BeCl+. The chlorocarbon
intermediates in the top spectra using CCl4 have been identified
in previous work starting with CCl3 radical and cation.39
Figure 8 presents the analogous results using argon as the
matrix host. The major triplet product starts at 1111.5 cm−1,
and the components are within 0.1 cm−1 of the values in Figure
6. The doublets for BeCl and HBeCl are well-resolved and
indicative of a single Cl atom vibration (Table 2). The band
marked BeCl+ shifts to 995.9 cm−1 in solid argon. Two
additional bands are observed in the SiCl4 experiment labeled
HBeCl, one in the Be−H stretching region at 2117.6 cm−1
below BeH2 at 2159.1 cm−1 first produced from the Be plus H2
reaction40 and one lower in the region for HBeCl bending. In
addition H35Cl, H37Cl was observed at 2887.7, 2885.5 cm−1
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(not shown). To verify that HBeCl is formed through the
reaction with HCl from the hydrolysis of SiCl4 during sample
preparation, the vacuum manifold was passivated with D2O
overnight, and new SiCl4 samples were prepared and evacuated
until a clean spectrum containing DCl at 2079.1, 2076.3 cm−1
could be formed from the hydrolysis of SiCl4 with D2O. A
spectrum showing new chlorine isotopic absorptions for DBeCl
at 768.6 and 763.7 cm−1 is compared in Figure 9 with expanded
absorbance scale spectra from Figure 8. Weaker HBe35Cl and
HBe37Cl bands are still observed in the spectrum using D2O at
800.4 and 795.6 cm−1 without any intermediate bands, which
confirms the presence of a single H or D atom in this product
molecule. The HBeCl and DBeCl bands increase slightly on
annealing and irradiation. Notice that the BeCl doublet is not
shifted using D2O to make the sample.
The CCl4 experiment also reveals a number of chlorocarbon
intermediates produced by ablation plume photolysis of CCl4
again featuring CCl3 radical and cation and CCl3−Cl.41−45
These absorptions have been observed using different metal
ablations with CCl4 in the sample, which illustrates the role of
laser plume photolysis on the matrix samples.20,45
Figure 10 shows the spectra in krypton matrixes, and Table 2
lists the observed frequencies. The strong BeCl2 triplet is
observed beginning at 1102.5 cm−1 and is in excellent
agreement with the peaks in Figure 6. Three bands were
again observed for HBeCl in the SiCl4 experiment along with
HCl at 2873.2, 2970.3 cm−1 (not shown), and the SiCl3 radical
is observed at 580 cm−1.35
Figure 11 illustrates infrared spectra in xenon matrixes using
the Be reaction with the CCl4 and SiCl4 reagents. The BeCl2
peak at 1096.1 cm−1 is broader, and the isotopic components
are not resolved. However, the BeCl absorption is a resolved
doublet at 811.5, 806.3 cm−1, but a site splitting may contribute
to the lower peak as its intensity exceeds that for a single Cl
atom vibration with natural abundance isotopes. The SiCl4
experiment reveals weaker HBeCl bands and a weaker HCl
band at 2858.6 cm−1 than with the lighter matrixes. Finally,
Figure S3 compares the Be reactions with SiCl4 in the four
noble gas matrixes.
Figure 9. Infrared spectra in the product absorption regions for laser-
ablated Be atoms and cations codeposited with SiCl4 or SiCl4/D2O in
excess argon at 4 K: (a) Be + 0.5% SiCl4/D2O in Ar codeposited for 60
min, (b) after annealing to 25 K, (c) after photolysis with λ > 220 nm
for 10 min; (d) Be + 0.1% SiCl4 in Ar codeposited for 60 min, (e) after
annealing to 25 K, (f) after photolysis with λ > 220 nm for 10 min.
Finally the optimized structures for product molecules based
on B3LYP/6-311++g(3df,3pd)/sdd, B3LYP/cc-pVTZ, and
CCSD(T)/cc-pVTZ level calculations are illustrated in Figure
12.
Figure 10. Infrared spectra in the product absorption regions for laser-ablated Be atoms and cations codeposited with SiCl4 or CCl4 in excess
krypton at 4 K: (a) Be + 0.1% SiCl4 in Kr codeposited for 60 min, (b) after annealing to 25 K, (c) after photolysis with λ > 220 nm for 10 min, (d)
after annealing to 35 K; (e) Be + 0.1% CCl4 in Kr codeposited for 60 min, (f) after annealing to 25 K, (g) after photolysis with λ > 220 nm for 10
min, (h) after annealing to 35 K.
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Figure 11. Infrared spectra in the product absorption regions for laser-ablated Be atoms and cations codeposited with SiCl4 or CCl4 in excess xenon
at 4 K: (a) Be + 0.1% SiCl4 in Xe codeposited for 40 min, (b) after annealing to 25 K, (c) after photolysis with λ > 220 nm for 10 min, (d) after
annealing to 35 K; (e) Be + 0.01% CCl4 in Xe codeposited for 40 min, (f) after annealing to 25 K, (g) after photolysis with λ > 220 nm for 10 min,
(h) after annealing to 35 K.
Assignments for Beryllium Dihalides. The agreement of
our strong BeF2 absorptions from Be atom reactions with F2,
ClF, CF2Cl2, and NF3 in solid Ne, Ar, and Kr within 2 cm−1 of
measurements made for the solid BeF2 evaporation product
trapped in these matrixes12 substantiates our assignments. This
identification of BeF2 is confirmed by B3LYP and CCSD(T)
calculated frequencies (Table 3), which are 1.2, 1.9, and 2.5%
higher than the observed value in solid Ne, respectively; the
B3LYP value is 2.3% higher than the solid Ar observation and
2.6% higher than the solid Kr measurement, which are excellent
for these levels of theory.20,28,29 Some of this discrepancy is due
to anharmonicity in the observed frequencies not accounted for
in the harmonic calculations.
interactions involving the Ng-BeO complexes.2,11 Clearly the
large charge on the Be center is paramount for these ion−
dipole interactions. The Mulliken charges on BeO and its Ng
complexes are given in Table S2. These charges from B3LYP/
cc-pVTZ are 0.31 for BeO itself and 0.20, 0.12, 0.09, and
−0.02 for the Ng complexes. The intermatrix shifts in the
frequencies (Ne−Ar, Ar−Kr, Kr−Xe) are 12.6, 4.3, and 5.1
cm−1, respectively, where the largest difference between
matrices is for Ne and Ar. We now make the same comparisons
with the Be halides.
The linear FBeF molecule has the largest positive Mulliken
charge (q) of any of our neutral molecules (Table 4). We
presume that the CCSD(T) charges are more accurate than the
DFT values, so we are looking at a q(Be) value of 0.706 on the
Be, which is supported by two fluorides of −0.353 charge. This
large charge at the Be center can sustain charge-induced dipole
interactions with a number of matrix atoms, and this provides a
reasonable rationale for the above series of blue matrix shifts for
this linear molecule. The BeF2 molecule has 17.1 and 3.6 cm−1
shifts between Ne to Ar and Ar to Kr, and we find that the Ne−
Ar separation is largest for all of the product molecules in
Tables 1 and 2, and this difference is most pronounced for the
BeF stretching modes of BeF2 and BeClF (16.3 and 4.3 cm−1),
which has the second-largest q(Be). The large Ne-to-Ar shift
can be attributed to the largest relative change in polarizability
for the matrix atoms (Ne, 2.67; Ar, 11.1; Kr, 16.7; Xe, 27.3 in
atomic units),46 where the atomic polarizability increases by a
factor of 11.1/2.67 = 4.2 from Ne to Ar and only 16.7/11.1 =
1.5 for Ar relative to Kr.
The highest band at 1529.4 cm−1 in solid argon is close to
the 1528 cm−1 assignment of Snelson to BeF2, and the weak
band in Figure 3 at 1246 cm−1, which also increased on
photolysis, is in agreement with that reported later by Snelson
for (BeF2)2.12,36 Our calculations for the singlet rhombic ring
structure suggested by Snelson et al.33 find the strongest band
at 1273 cm−1 with 824 km/mol intensity, which substantiates
these assignments.
The krypton matrix presents a new absorption at 1525.8
cm−1 for BeF2 along with a higher band at 1541.5 cm−1 also
observed by Snelson.12 This higher band is probably due to an
unusual matrix site like a BeF2 molecule on the surface of a
microcrystal. Recall that krypton has a much higher freezing
point than argon and neon, and Kr will freeze more quickly and
not as well annealed as the lighter noble gases even though we
condensed our Kr samples at 17 1 K.
The three matrix values for the antisymmetric F−Be−F
stretching mode are all above the 1520 cm−1 gas-phase
measurement,13 which is not the typical behavior for matrix-
isolated molecules.38 However, this relationship has been
reported for noble gas complexes of BeO in matrices,2 and
our recent observation of BeO in neon at 1538.7 cm−1
(unpublished results) has been attributed to induced-dipole
In the case of BeCl2 we have agreement within 2 cm−1 for
measurements made for the product molecule from Be
reactions with Cl2, ClF, CF2Cl2, CCl4, and SiCl4, and within
4 cm−1 of values from the evaporation of solid BeCl2.12 In
addition we have resolution of natural abundance chlorine
isotopic triplets with ∼9/6/1 relative intensities (Figure 6) for a
molecule with two equivalent Cl atoms. The stepwise decreases
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Figure 12. Optimized structures for product molecules based on B3LYP/6-311++g(3df,3pd)/sdd, B3LYP/cc-pVTZ (italic), and CCSD(T)/cc-
pVTZ level (bold). Bond lengths are in angstroms, and bond angles are in degrees.
in the strong antisymmetric stretching mode for BeCl2 in solid
Ne, Ar, Kr, and Xe (13.6, 8.9, and 6.4 cm−1) are less than the
first and more than the second intermatrix shifts for BeF2, but
the total Ne-to-Kr shift for BeCl2, 22.5 cm−1, is slightly larger
than this value for BeF2, 20.7 cm−1, in spite of the much smaller
q(Be) for BeCl2, which is half of that calculated for BeF2. We
find that only the neon matrix fundamental, 1125.2 cm−1, is
above the gas-phase frequency, 1113 cm−1.13 The B3LYP
frequencies for BeCl2 are only 8 and 9 cm−1 higher (0.7and
0.8%), the CCSD(T) frequency is 19 cm−1 (1.8%) higher than
the neon matrix values, and the calculated and observed
chlorine isotopic splittings are the same (1.7 cm−1) within 0.1
cm−1.
Our Be reactions with ClF and with Cl2/F2 mixtures enabled
the formation of BeClF through the two different reaction
pathways given above. On first thought the “antisymmetric”
Cl−Be−F stretching mode might fall close to the averages of
these two modes for BeF2 and BeCl2, which are 1336 cm−1 for
neon and 1321 cm−1 for argon and somewhat lower than the
observed values of 1391.9 and 1375.6 cm−1 in these two
matrixes. However, the B3LYP calculated frequency for BeClF
Table 4. Calculated Mulliken Charges for BeF, BeF2, BeCl,
BeCl2, FBeCl, and HBeCl
a
q(Be)
q(F)
q(F)
q(Be)
q(Cl)
BeF
0.323
0.231
0.349
1.020
0.492
0.706
q(Be)
−0.323
−0.231
−0.349
−0.510
−0.246
−0.353
q(Cl)
FBeCl
−0.497
−0.252
−0.372
0.887
0.341
0.498
−0.390
−0.089
−0.125
BeF2
q(H)
q(Be)
q(Cl)
BeCl
0.361
0.071
0.126
0.822
0.238
0.350
−0.361
−0.071
−0.126
−0.411
−0.119
−0.175
HBeCl
−0.147
−0.058
−0.113
0.528
0.140
0.246
−0.381
−0.082
−0.133
BeCl2
a
Calculated with B3LYP/6-311++G(3df,3pd) level, B3LYP/cc-pVTZ
level (italic), and CCSD(T)/cc-pVTZ level (bold).
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is 1399.8 cm−1, only 8 cm−1 higher than the neon matrix value
with only a 0.6 cm−1 separation for the chlorine 35 and 37
isotopes. This frequency is a mostly Be−F stretching mode
with the largest computed intensity (403 km/mol) for any of
our major products. The more symmetric Be−Cl counterpart
computed at 521.5 cm−1 with a 6.0 cm−1chlorine isotopic shift
has a very low intensity (5 km/mol) and is a mostly Be−Cl
stretching mode. The intermatrix Ne−Ar and Ar−Kr shifts
(16.3 and 4.3 cm−1) for BeClF are nearly the same as found for
BeF2, although the q(Be) is slightly lower than the average of
the q(Be) for the difluoride and dichloride. Agreement with the
computed values for this strong Be−F stretching mode for
BeClF confirms the identification of this new molecule. The
small splitting of 1.4 cm−1 on the 1391.9 cm−1 band is a matrix
splitting, since it is too much for the separation of chlorine
isotopes.
Finally, a similar experiment was performed with Be and
CF2Cl2 in argon, and the infrared spectra are illustrated in
Figure S2. Remembering that C−Cl bonds are weaker than C−
F bonds, we find the BeCl2 absorption at 1111.5 cm−1 to be
considerably stronger than the BeF2 band at 1529.1 cm−1, but
the sharp BeClF band at 1375.5 cm−1 in this experiment was
stronger than both of the former. And the 1206.6 cm−1 CF2Cl
band was stronger than the 918.3 cm−1 shoulder absorption for
CFCl2, where these radicals were likely produced by laser
ablation plume photolysis.20,35 Both BeF and BeCl were
observed and decreased on photolysis as will be described
below. These frequencies are gathered in Table S3.
to be at 777.5 and 772.5 cm−1, which is in excellent agreement
with the observed values, and confirms the identification of
HBeCl and DBeCl. Similar behavior was found for these bands
shifted 4−6 cm−1 in a krypton matrix. This Be insertion
reaction is exothermic by 85 kcal/mol.
(6)
Be + HCl → HBeCl
Assignments for Diatomic Beryllium Fluoride and
Chloride. The 1242.2 cm−1 (1241.6 matrix site) band in neon
and its argon (1234.8 cm−1) and krypton (1229.7 cm−1) matrix
counterparts decreased on UV photolysis, while the strong
BeF2 absorption increases. They were formed using both the F2
and NF3 reactions with Be, and almost the same feature, 1233.1
cm−1, was observed from CF2Cl2 without OCF2 nearby (Table
S3). The former bands range from 13.1 to 5.7 to 0.6 cm−1
higher, respectively, than the gas-phase frequency (1229.1
cm−1) for BeF.9 Our calculations predict slightly higher
frequencies as expected. The B3LYP functional gives 1249.8
and 1257.0 cm−1 with two different basis sets, and the
CCSD(T) method obtains 1260.5 cm−1, which are quite
reasonable agreements with experiment for harmonic frequency
calculations. Although we were not able to compute binding for
a single Ng atom to BeF like we did for the cation below, the
q(Be) computed (Table 4) for BeF, 0.349, is sufficient to
support a stronger than typical interaction with the surrounding
matrix atoms to explain the blue matrix shifts above for Ne, Ar,
and Kr. BeCl has a much lower q(Be), 0.126, and the matrix
shifts are all to the red of the gas phase, which is the expected
relationship.
Assignments for Beryllium Hydrogen Chloride. First,
examine the sharp 3/1 relative intensity doublet at 800.4 and
795.6 cm−1 in the argon matrix containing SiCl4, which
increases 10% upon annealing to 25 K, another 10% on broad-
band irradiation, and decreases 20% in final annealing to 35 K
(Figures 8 and 9). Two other bands at 2117.6 and 515.6 cm−1
exhibit the same behavior, and they are associated with the
same new molecule, which contains a single Cl atom based on
the sharp resolved 3/1 doublet just below the BeCl doublet at
817.7, 813.4 cm−1. The strong band at 2117.6 cm−1 falls just
below BeH2 in the Be−H stretching region,40 so we have a new
molecule containing Be−H and Be−Cl bonds. The D2O doped
experiment revealed a counterpart for DBeCl at 1613.1 cm−1,
and this HBeCl/DBeCl ratio 1.313 is near the calculated mode
ratio 1.324 for these two product molecules and the 1.333 ratio
observed for BeH/BeD.40 Both B3LYP calculations predict the
three strong IR absorptions for HBeCl (Table 3) slightly higher
than the three argon matrix bands, and the CCSD(T) does so
for the two higher modes, but the lowest mode is 3.8 cm−1
lower. Furthermore, the calculations predict 4.9 and 5.0 cm−1
chlorine isotopic components compared with the observed 4.8
cm−1 value in solid argon. This frequency agreement is
excellent, and it confirms the identification of HBeCl. The
doublet at 800.4, 795.6 cm−1 shifts to 768.6, 763.7 cm−1 when
D2O was introduced into the sample manifold, as shown in
Figure 9, and DCl was formed from the hydrolysis of SiCl4.
This shift also confirms that H/D is involved with these
chlorine isotopic doublets having 4.8 and 4.9 cm−1 splittings,
and our calculations predicted 5.0 cm−1. The similar HBeNC
molecule has three strong modes at 2153.2, 912.4, and 525.4
cm−1, and the highest (Be−H stretch)7 and lowest (H−Be−Cl
or H−Be−N bending) modes are comparable. Finally, the first
intermatrix shift for HBeCl, 11.4 cm−1, is smaller than those
described above for the beryllium dihalides. Our B3LYP
calculations predicted these chlorine isotopic bands for DBeCl
The BeCl chlorine isotopic doublets in Table 2 clearly
demonstrate in the argon matrix spectra in Figures 8 and 9 that
one chlorine atom is involved in this vibration, and the
measured isotopic separation of 4.3 cm−1 agrees with the
computed values as do the frequencies themselves (compare
Tables 2 and 3). The neon matrix value is 3.9 cm−1 below the
gas-phase value (836.7 cm−1),9 and the heavier matrix values
fall steadily lower than the neon matrix observation. This is the
expected behavior for a matrix-isolated molecule.38 The
splitting in xenon involves a matrix site as well as Be37Cl.
Assignments and Bonding for Beryllium Fluoride and
Chloride Cation Complexes. The matrix spectra for the
SiCl4 reaction with Be and the Ne and Ar matrix spectra for
CCl4 reveal bands labeled NeBeCl+ and ArBeCl+. These bands
share the common behavior of slightly increasing on annealing
and decreasing slightly on photolysis. A 996.4 cm−1 band with a
994.8 cm−1 shoulder in the argon matrix from the Be and Cl2
reaction behaves the same way as does the neon matrix
counterpart at 1001.4 cm−1. The broader absorption at 1445.0
cm−1 in solid argon, which increases slightly on photolysis and
sample annealing, and our DFT calculations revealed a very
strong band at 1457.7 cm−1 for the Be−F stretching mode of
BeF+ and of Ar-BeF+ with the latter 50% stronger. It is
interesting to note that an experiment with 1.3% each of Kr and
F2 in argon gave the same BeF2 peak as pure argon, but the
BeF+ peak was shifted to 1444.7, and the BeF peak shifted to
1234.1 cm−1. This suggests that FBeF is not as sensitive to the
noble gas environment as BeF and BeF+, and it follows that the
Be centers in these diatomics have more room for interaction
with the noble gas matrix than does FBeF. The cation peaks are
labeled NgBeF+ or NgBeCl+ in the figures, because we believe
that one noble gas atom binds strongly with BeF+ and BeCl+.
The calculated ionization energies for these diatomic molecules
are 235.4 and 230.1 kcal/mol and 225.8 and 222.5 kcal/mol
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Table 5. Calculated Vibrational Frequencies (cm−1), Bond Lengths, Dipole Moments, Mulliken Charges, and Binding Energies
a
for BeF+ and NgBeF+ (Ng = Ne, Ar, Kr, Xe)
Mulliken charge
frequency(Be−F, cm−1
)
R(Ng−Be, Å)
dipole moment (D)
q(Ng)
q(Be)
q(F)
Do (Ng−BeF+, kcal·mol−1
)
BeF+
1457.7(255)
1452.6(252)
1445.8
7.62
7.60
8.20
3.36
3.30
4.66
2.63
2.54
2.90
0.88
0.81
1.11
0.36
0.28
0.56
1.07
1.06
1.19
1.15
0.86
1.03
0.90
0.67
0.83
0.86
0.60
0.76
0.61
0.55
0.67
−0.07
−0.06
−0.19
−0.12
−0.07
−0.20
−0.21
−0.12
−0.25
−0.38
−0.13
−0.26
−0.21
−0.15
−0.27
NeBeF+
ArBeF+
KrBeF+
XeBeF+
1472.5(315)
1469.8(313)
1469.5
1.676
1.674
1.672
1.970
1.969
1.968
2.114
2.112
2.102
2.300
2.298
2.282
0.02
0.22
0.17
0.31
0.45
0.42
0.42
0.53
0.50
0.60
0.60
0.60
12.1
29.2
34.8
41.4
1457.7(374)
1461.4(371)
1466.3
1444.4(387)
1450.6(384)
1459.9
1433.2(400)
1437.0(396)
1448.0
a
Calculated with B3LYP/6-311++G(3df,3pd)/sdd level and B3LYP/cc-pVTZ/sdd level (italic), and CCSD(T)/cc-pVTZ level (bold).
Table 6. Calculated Vibrational Frequencies (cm−1), Bond Lengths, Dipole Moments, Mulliken Charges, and Binding Energies
a
for BeCl+ and NgBeCl+ (Ng = Ne, Ar, Kr, Xe)
Mulliken charge
frequency(Be−Cl, cm−1
)
R(Ng−Be, Å)
dipole moment (D)
q(Ng)
q(Be)
q(Cl)
Do (Ng−BeCl+, kcal·mol−1
)
BeCl+
1014.7(201)
1009.5(200)
1007.0
8.02
8.07
8.83
4.56
4.60
5.13
3.90
3.91
4.39
1.63
1.67
2.02
0.78
0.83
1.27
1.05
1.25
0.72
1.01
0.50
0.61
0.85
0.38
0.46
0.74
0.32
0.42
0.62
0.25
0.32
−0.05
−0.25
0.27
NeBeCl+
ArBeCl+
KrBeCl+
XeBeCl+
1075.8(296)
1075.9(297)
1080.1
1.683
1.674
1.671
1.972
1.974
1.972
2.119
2.118
2.106
2.305
2.303
2.293
0.03
0.20
0.16
0.28
0.41
0.39
0.42
0.50
0.48
0.55
0.59
0.58
−0.04
0.29
11.3
26.9
32.1
38.0
0.23
1078.5(363)
1076.7(366)
1087.2
−0.14
0.21
0.14
1065.8(377)
1062.9(380)
1080.3
−0.16
0.18
0.10
1055.3(390)
1051.3(389)
1066.6
−0.17
0.15
0.09
a
Calculated with B3LYP/6-311++G(3df,3pd)/sdd level, B3LYP/cc-pVTZ level (italic), and CCSD(T)/cc-pVTZ level (bold).
using B3LYP and CCSD(T), respectively, and the Ng atoms
used here have higher first ionization energies, from Ne to Xe,
namely, 497, 363, 323, and 280 kcal/mol, respectively, which
are more than our computed values for BeF and BeCl. Clearly
some positive charge will transfer to the Ng atoms. Our
computed Mulliken charges, dipole moments, and Be−X
stretching frequencies are listed in Tables 5 and 6. As we
proceed down the noble gas family the lower Ng ionization
energies sustain more positive charge on the Ng atom, the
dipole moments decrease, and the Xe and Be charges become
more nearly equal, which indicates the decrease of ionic
character between Ng and Be. This change follows a decrease in
the positive q(Be), while positive q(Ng) increases. For the
purpose of understanding the interaction of Ng and Be, an
effective method, the noncovalent interaction index (NCI)
based on the relationship between the electron density ρ(r) and
the reduced density gradients has been introduced to study
such weak long-range interation.35 As depicted in Figure S4, a
spike corresponding to Ne−Be located at −(λ2)ρ (∼0.045,
lower than 0.050) in the plot of NeBeF+ shows stronger
noncovalent interaction, while larger value of −(λ2)ρ (∼0.057,
a little higher than 0.050) in the plot of NgBeF+ (Ng = Ar, Kr,
Xe) (Xe, not shown) suggests a weak covalent interaction.
As described in the introduction based on the Beauchamp
investigations14,15 (and others) laser ablation generates positive
metal ions and electrons,16 and we believe that vacuum UV
radiation in the ablation plume is capable of photoionization of
some metal atoms. Therefore, if Be+ reactions form molecular
cations with strong infrared intensities then these positive ions
can be observed in the matrix infrared spectrum. Note that the
infrared intensity for BeF+ increases in the Ng-BeF+ species as
Ng moves from Ne to Xe (Table 5). So the first three reactions
with Be+ occur directly on deposition. Charge balance is
assured by the ready formation of F− and Cl− in these
experiments. The F3− anion, which could not be observed here
because of instrument low-frequency limitation, is commonly
observed in fluorine experiments with laser-ablated metals.47
However, we do observe a weak band at 1378 cm−1 in solid
K
DOI: 10.1021/acs.jpca.7b09454
J. Phys. Chem. A XXXX, XXX, XXX−XXX

The Journal of Physical Chemistry A
Article
argon, which is probably due to HF2 (not shown).35 In
which reacts with HCl to form the stable HCl2− anion. Finally,
−
−
−
addition, the stable HCl2 anion was formed through the
BeX3− anions are also stable, and tentative identifications of
reaction of HCl with Cl−, and its two characteristic absorptions
were observed at 696 and 956 cm−1 in solid argon. These bands
were much stronger in the SiCl4 than in the CCl4 experiments
BeF3 and BeCl3 are proposed.
−
ASSOCIATED CONTENT
* Supporting Information
■
−
(Figure 8). Note that the HCl2 band increases on annealing
S
and photolysis in the latter experiments. Only the stronger 738
cm−1 band was observed in solid neon.35,48,49 Reaction 7 is
exothermic by 25 kcal/mol (B3LYP/6-311++g(3df,3pd)).
−
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.jpca.7b09454.
Calculated vibrational frequencies, intensities, and
Cartesian coordinates of the observed products. Infrared
spectra using ClF and CF2Cl2 precursors (PDF)
HCl + Cl− → HCl2
(7)
In the search for new molecules that might be produced in
−
−
these experiments, we found that BeF3 and BeCl3 are stable
to halide ion elimination by 87 and 56 kcal/mol, respectively,
with strong stretching absorptions computed at 1049.6 cm−1
(346 × 2 km/mol) and 718.7, 715.9 cm−1 (316, 313 km/mol).
The weak band at 705.6 cm−1 in solid argon is tentatively
assigned to BeCl3 . We did not detect HF2 , but a weak band
(0.0023 au) in neon experiments at 1061.4 cm−1 (not shown)
decreases 10% on UV photolysis and increases 20% on
AUTHOR INFORMATION
Corresponding Authors
*E-mail: xfwang@tongji.edu.cn. (X.W.)
*E-mail: lsa@virginia.edu. (L.A.)
■
−
−
ORCID
Lester Andrews: 0000-0001-6306-0340
Xuefeng Wang: 0000-0001-6588-997X
Notes
−
annealing to 10 K, which can be assigned tentatively to BeF3
in these experiments.
The authors declare no competing financial interest.
Be+ + X2 → [BeX2+]* → BeX+ + X
(8)
ACKNOWLEDGMENTS
Be+ + X → [BeX+]* → BeX+
■
(9)
This work was supported by the National Natural Science
Foundation of China (No. 21373152). We thank J. Thrasher
for the F2 and ClF samples.
Ng + BeX+ → Ng − BeX+
(10)
+
Be+ + X2 → [BeX2+]* → BeX2
(11)
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■
−
BeX2 + X− → BeX3
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