Infrared Spectra of Thallium Hydrides in Solid Neon, Hydrogen, and Argon

Article abstract of DOI:10.1021/jp0498973

Laser-ablated Tl atoms react with dihydrogen in excess neon, pure hydrogen, and excess argon to form primarily the TlH diatomic molecule. Ultraviolet irradiation increases weak bands that are identified as TlH₂ and TlH₃ on the basis of D₂ and HD substitution and density functional theory (DFT) isotopic frequency calculations. Sample annealing fosters the dimerization of TlH to give Tl₂H₂ with a rhombic ring structure and the TlTlH₂ isomer. The markedly lower yield of TlH₃ in these experiments compared to AlH₃ in earlier investigations is due to the expected decrease in stability for the Tl(III) oxidation state. The Tl⁺(H₂)_n cation complex is also observed, and trends within the group 13 metals are summarized. Excitation at 193 nm gives the ²S_1/2 → ²P_1/2,3/2 doublet for unreacted Tl atoms, which is blue-shifted 660 cm^-1 from the gas-phase value in solid D₂ but only 210 cm_-1 in solid H₂, owing to the smaller, more repulsive D₂ matrix cage.

Full text of DOI:10.1021/jp0498973

3396
J. Phys. Chem. A 2004, 108, 3396-3402
Infrared Spectra of Thallium Hydrides in Solid Neon, Hydrogen, and Argon
Xuefeng Wang and Lester Andrews*
Department of Chemistry, UniVersity of Virginia, McCormick Road, P.O. Box 400319,
CharlottesVille, Virginia 22904-4319
ReceiVed: January 8, 2004; In Final Form: February 10, 2004
Laser-ablated Tl atoms react with dihydrogen in excess neon, pure hydrogen, and excess argon to form primarily
the TlH diatomic molecule. Ultraviolet irradiation increases weak bands that are identified as TlH2 and TlH3
on the basis of D2 and HD substitution and density functional theory (DFT) isotopic frequency calculations.
Sample annealing fosters the dimerization of TlH to give Tl2H2 with a rhombic ring structure and the TlTlH2
isomer. The markedly lower yield of TlH3 in these experiments compared to AlH3 in earlier investigations is
due to the expected decrease in stability for the Tl(III) oxidation state. The Tl+(H2)n cation complex is also
2
observed, and trends within the group 13 metals are summarized. Excitation at 193 nm gives the S1/2
f
2P1/2,3/2 doublet for unreacted Tl atoms, which is blue-shifted 660 cm-1 from the gas-phase value in solid D2
but only 210 cm-1 in solid H2, owing to the smaller, more repulsive D2 matrix cage.
Introduction
Small group 13 metal hydrides have been investigated
extensively (M ) Al, Ga, or In), including by gas-phase
spectroscopy for the monohydride diatomics1-9 and matrix
infrared studies for the mono-, di-, and trihydrides, which reveal
increasing frequencies in the MH1,2,3 series for each metal.10-18
Electron spin resonance has been employed to investigate the
AlH2 radical in solid neon.19 The M2H2 and M2H6 species have
been characterized by increasing stability of the former and
decreasing stability of the latter with the heavier metals.
Thallium hydride, TlH, has only been investigated in the gas
phase,1,20 and by theoretical calculations,21-24 and there is no
experimental evidence to date for TlH2 and TlH3, although the
latter have also been subjected to theoretical calculations as
heavy metal compounds, owing to interest in relativistic
effects.25,26 The trend of decreasing stability for the heavier metal
trihydride is manifest in the lower yield of InH3 relative to
AlH3,18 and this points to difficulty for the preparation of TlH3.
Figure 1. Infrared spectra in the 1780-1260 cm-1 region for normal
hydrogen co-deposited at 3.5 K with laser-ablated thallium. Spectra of
H2 + Tl: (a) before irradiation, (b) after 15 min of λ > 240 nm
irradiation, (c) after 15 min more of λ > 240 nm irradiation, (d) after
annealing to 6.0 K, and (e) after annealing to 6.5 K.
Experimental and Theoretical Methods
Density functional theory (DFT) frequency calculations were
helpful in assigning lead and bismuth hydride spectra,29,30 so
similar B3LYP/6-311++G**/Stuttgart scalar relativistic pseudo-
potential for Tl together with the corresponding basis set (SDD)
calculations were performed for thallium hydrides using the
Gaussian 98 program system.31-33 Comparable results were
obtained using the BPW91 functional.34 Although these calcula-
tions are only approximate, they provide a useful guide for
assigning vibrational spectra.
The laser-ablation matrix-isolation infrared spectroscopy
experiment has been described previously.27,28 Briefly, the Nd:
YAG laser fundamental (1064 nm, 10 Hz repetition rate, 10 ns
pulse width) was focused on rotating a high purity thallium
(Spex Industries, 99.999%) target using 5-20 mJ/pulse, and
thallium atoms were co-deposited with pure H2 or D2 (Mathe-
son), pure HD (Cambridge Isotope Laboratories), and neon or
argon diluted samples onto a CsI window cooled to 3.5 K by a
Sumitomo Heavy Industries RDK-205D cryocooler. Infrared
spectra were recorded in a Nicolet 750 Fourier transform
instrument at 0.5 cm-1 resolution using a liquid-nitrogen cooled
MCTB detector after deposition, annealing, and filtered mercury
arc or 193 nm laser (Lambda Physik, Optex) irradiation.
Emission spectra were recorded using an Ocean Optics optical
fiber spectrometer.
Results
Reaction products from laser-ablated Tl and dihydrogen
trapped in excess hydrogen, neon, and argon and supporting
DFT calculations will be presented.
Hydrogen. Laser-ablated Tl co-deposited with hydrogen
(deuterium) produces weak bands at 1311 (940) cm-1 that
increase upon ultraviolet irradiation to strong bands at 1311.3
(939.9) cm-1, as shown in Figure 1 (Figure 2). This treatment
* To whom correspondence should be addressed. E-mail: lsa@
virginia.edu.
10.1021/jp0498973 CCC: $27.50 © 2004 American Chemical Society
Published on Web 03/19/2004

Infrared Spectra of Thallium Hydrides
J. Phys. Chem. A, Vol. 108, No. 16, 2004 3397
Figure 2. Infrared spectra in the 1300-900 cm-1 region for normal
deuterium co-deposited at 3.5 K with laser-ablated thallium. Spectra
of D2 + Tl: (a) before irradiation, (b) after 15 min of λ > 240 nm
irradiation, (c) after 15 min more of λ > 240 nm irradiation, (d) after
annealing to 8.0 K, and (e) after annealing to 9.0 K.
Figure 3. Infrared spectra in the 1800-800 cm-1 region for pure HD
co-deposited at 3.5 K with laser-ablated thallium. Spectra of HD +
Tl: (a) before irradiation, (b) after 30 min of λ > 240 nm irradiation,
(c) after annealing to 7.3 K, (d) after 15 min of λ > 240 nm irradiation,
and (e) after annealing to 8.0 K.
also yields new absorptions at 1519.9 (1098.8) and 1390.2
(1007.6) cm-1 and weak bands at 1748.4 (1254.4) cm-1
.
and 3972 (2870) cm-1 16-18
. The spectra in Figure 4 show that
Annealing increases the strong bands and new features at 1424.3
(1020.5) cm-1. Weak bands also appear upon annealing at 908.8
(653.1) cm-1 that are produced in greater yield using neon host
matrixes. Table 1 lists the observed frequencies.
The HD experiment provides important diagnostic informa-
tion on the thallium hydrides in Figure 3. The strong initial bands
are observed slightly shifted in the pure HD host at 1320.1 and
945.9 cm-1. The sharp 1519.9 (1098.8) and 1390.2 (1007.6)
cm-1 bands are replaced by a new set at 1461.8 and 1046.2
cm-1. The weaker 1748.4 (1254.4) cm-1 absorptions shift to
1747.3 and 1258.1 cm-1. Finally, a weak 839.0 cm-1 band is
observed instead of the 908.8 (653.1) cm-1 pair.
λ > 240 nm irradiation effectively destroys all product bands
in this region. However, in the more robust deuterium lattice,
the 2870 cm-1 absorption for (D-)(D2)n is regenerated in part
by 193 nm irradiation: this destruction-regeneration cycle is
repeated. Likewise, the higher frequency region with HD shows
analogous sharp bands at 3621.7 and 3596.3 cm-1 and a broader
feature at 3478 cm-1. The sharp 3621.7 cm-1 and broad 3478
cm-1 bands are common to other metal experiments with HD.
Neon. Weak bands are observed at 1327 (950) cm-1 for H2
(D2) in excess neon co-deposited with Tl atoms. Spectra in
Figure 5 compare deposited samples after deposition and 193
nm irradiation (5 min at 4 mJ/pulse). Stronger bands at 919.8
(667.3) cm-1 acquire a 851.1 cm-1 HD counterpart. Irradiation
also produces weaker 1525.9 (1103.5) cm-1 bands with a 1468
cm-1 HD counterpart.
The higher frequency region for hydrogen (deuterium) reveals
sharp new 4113.6 (2962.8) cm-1 absorptions and other metal
independent absorptions observed previously at 4143.4 (2982.4)
TABLE 1: Infrared Absorptions (cm-1) Observed from Reaction of Thallium and Dihydrogen in Neon, Hydrogen, and Argon
neon
HD
hydrogen
HD
argon
HD
H2
D2
H2
D2
H2
D2
identity
4113.6
1748.4
3596.3
1747.3
1259.9
2962.8
Tl+(H2)n
TlH3
TlD3
anneal pdt
anneal pdt
TlH2 (site)
TlH2
1254.4
1224.3
1700.2
1522.4
1519.9
1525.9
1503.3
1468
1461.8, 1046.2
TlHD
1112.3
1103.5
1101.4
1098.8
TlD2 (site)
TlD2
TlH2 (site)
TlH2
1082.0
1394.7
1390.2
1010.3
1007.6
TlD2 (site)
TlD2
1430.3
1424.3
1430.8
1424.8
1424.2, 1423.0
1023.9, 1022.6
1023.5
1027.7
1339.6
1320.1
959.4
TlTlH2 (site)
TlTlH2
TlTlHD
TlTlHD
TlTlD2 (site)
TlTlD2
TlH (site)
TlH
TlD (site)
TlD
Tl2H2
Tl2HD
Tl2D2
1431.7
1427.6
1021.6
1020.5
1328.0
1311.3
1327
1327
950
1309.4
888.2
1309.4
938.0
953.4
939.9
950
945.9
938.0
642.6
919.8
908.8
888.0
825.3
642.8
851.1
839.0
667.3
653.1

3398 J. Phys. Chem. A, Vol. 108, No. 16, 2004
Wang and Andrews
Figure 6. Infrared spectra in the 600-1550 cm-1 region for hydrogen
co-deposited at 3.5 K with thallium in argon. Spectra of 4% H2 in argon
+ Tl: (a) before annealing and (b) after annealing to 30 K. Spectra of
3% HD in argon + Tl (10 mJ/pulse): (c) before annealing and (d)
after annealing to 30 K. Spectra of 6% HD in argon + Tl (30 mJ/
pulse): (e) before annealing and (f) after annealing to 30 K. Spectra
of 1.5% H2 + 1.5% D2 in argon + Tl: (g) before annealing and (h)
after annealing to 30 K. Spectra of 4% D2 in argon + Tl: (i) before
annealing and (j) after annealing to 30 K.
Figure 4. Infrared spectra in the H-H and D-D stretching regions
for hydrogen and deuterium co-deposited at 3.5 K with thallium. Spectra
of H2 + Tl: (a) before irradiation, (b) after 15 min of λ > 240 nm
irradiation, (c) after 15 min more of λ > 240 nm irradiation, (d) after
annealing to 6.0 K, and (e) after annealing to 6.5 K. Spectra of D2 +
Tl: (f) before irradiation, (g) after 15 min of λ > 240 nm irradiation,
(h) after 3 min of 193 nm irradiation (5 mJ/pulse at 10 Hz), (i) after λ
> 240 nm irradiation, and (j) after 4 min of 193 nm irradiation.
Figure 5. Infrared spectra in the 600-1550 cm-1 region for hydrogen
co-deposited at 3.5 K with thallium in neon. Spectra of 4% H2 in neon
+ Tl: (a) before irradiation and (b) after 5 min of 193 nm (5 mJ/pulse
at 10 Hz) irradiation. Spectra of 4% HD in neon + Tl: (c) before
irradiation and (d) after 193 nm irradiation. Spectra of 2% H2 + 2%
D2 in neon + Tl: (e) before irradiation and (f) after 193 nm irradiation.
Spectra of 4% D2 in neon + Tl: (g) before irradiation and (h) after
193 nm irradiation.
Argon. The weak argon matrix H2 (D2) reaction products at
1309.4 (938.0) cm-1 increase markedly upon annealing to allow
diffusion and reaction of trapped atomic species, as shown in
Figure 6a,b and i,j. Additional bands appear at 888.2 (642.6)
cm-1 upon annealing. Using the HD reagent, the latter two bands
plus a new 825.3 cm-1 absorption are produced: Increased laser
energy favors the yield of TlH and TlD, as illustrated in Figure
6c-f. The ArnH+ and ArnD+ species were also trapped in solid
argon.35,36
Emission Spectra. Emission spectra were recorded from the
1064 nm laser-generated plume above the target surface during
ablation-deposition. The strong Tl atomic spin-orbit doublets37
were observed at 377.7 and 535.2 nm and at 276.9 and 353.0
nm, as shown in Figure 7. In addition, weaker Tl+ lines were
found at 329.1, 507.7, 515.4, and 595.0 nm.38 During 193 nm
Figure 7. Emission spectra from hydrogen-thallium experiments: (a)
emission from the 1064 nm laser-ablation plume, (b) emission from
solid D2 + Tl using 193 nm excitation at 1 mJ/pulse, (c) emission from
solid H2 + Tl using 193 nm excitation at 1 mJ/pulse, (d) emission
from neon + Tl using 193 nm excitation, and (e) emission from argon
+ Tl using 193 nm excitation.
irradiation of the H2 and D2 samples, strong Tl atomic doublets
were observed at 374.7 and 526.2 nm and 368.5 and 513.8 nm,
respectively. Similar 193 nm irradiation of neon and argon
matrix samples containing Tl and H2 produced broader features
and sharper bands for atomic Tl at 548 nm in the former and
393 and 549 nm in the latter.

Infrared Spectra of Thallium Hydrides
J. Phys. Chem. A, Vol. 108, No. 16, 2004 3399
Discussion
Tl2H2 and TlTlH2. The large yield of TlH in these experi-
ments invites the consideration of dimers. On the basis of
observations for Ga2H2 and In2H2 and calculations from several
groups,41-45 the rhombic dimer is expected to be the minimum
energy structure and several higher energy isomers, including
TlTlH2, must be considered.
New thallium hydride absorptions will be assigned on the
basis of isotopic substitution, matrix shifts, and quantum
chemical calculations.
TlH. Experiments with laser-ablated Tl and hydrogen (deu-
terium) gave weak bands at 1311.3 (939.9) cm-1, which
increased markedly upon UV irradiation (Figures 1 and 2) and
are slightly lower than the gas-phase TlH (TlD) fundamentals1,20
of 1345.3 (963.7) cm-1 and are due to the diatomic hydride
molecules in solid H2 (D2). These TlH (TlD) bands are bracketed
by the argon matrix (1309.4 (938.0) cm-1) and neon matrix
(1327 (950) cm-1) values. Two sharp bands were observed with
pure HD, but both were blue-shifted 0.6% from the H2 (D2)
matrix values. Our simple B3LYP calculation predicts 1306
(926) cm-1 for these heavy metal hydride frequencies, which
is excellent, considering the approximations involved. The
BPW91 functional is slightly lower and not in as good
agreement.
TlH2. Weak sharp absorptions are produced at 1519.9
(1098.8) and 1390.2 (1007.6) cm-1 upon 193 nm irradiation of
solid hydrogen (deuterium) samples with H/D ratios of 1.383
and 1.380. The solid HD sample revealed sharp 1461.8 and
1046.2 cm-1 bands, which are 7 cm-1 above and below the
medians, respectively, for the two hydrogen and deuterium
modes. This substantiates assignment of the two bands to
antisymmetric and symmetric stretching modes of TlH2 (TlD2),
where interaction of the Tl-H and Tl-D stretching modes in
TlHD forces the two modes apart from the median TlH2 (TlD2)
values. The stronger antisymmetric mode is observed at 1525.9
cm-1 in solid neon and at 1503.3 cm-1 in solid argon, which
bracket the solid H2 value.
The evidence for Tl2H2 is summarized in Figure 5 for neon
experiments where the yield is high. The weak band at 919.8
cm-1 with H2 increases markedly upon 193 nm irradiation and
shifts to 677.3 cm-1 with D2 (H/D ratio: 1.378). Experiments
with a H2 + D2 mixture give primarily TlH, TlD, Tl2H2, and
Tl2D2 without evidence of the Tl2HD species. However, an
investigation with HD gives a strong intermediate band at 851.1
cm-1 and very weak Tl2H2 (Tl2D2) bands at 918.8 (653.1) cm-1
In solid argon, the yield of TlH is high after annealing and a
sharp doublet is observed for Tl2H2 at 897.0 and 888.2 cm-1
.
,
which shifts to 648.9 and 642.6 cm-1 with D2 (H/D ratios: 1.382
and 1.382). Using higher laser energy with HD (Figure 6e,f)
gives a large yield of TlH and TlD and a statistical yield of
Tl2H2, Tl2HD, and Tl2D2. However, using lower laser energy
with HD (Figure 6d,e) gives a small yield of TlH and TlD and
primarily Tl2HD at 833.0 and 825.3 cm-1
.
In solid molecular hydrogen, the weak 908.8 (653.1) cm-1
H2 (D2) bands are between solid neon and argon values, and
pure HD gives an intermediate 839.0 cm-1 band. Such is also
the case for In2H2.18,41
Our B3LYP calculations find a very intense b1u mode for
rhombic Tl2H2 at 915 cm-1, which is in excellent agreement
with the 918.8 cm-1 neon matrix observation. Stronger interac-
tions with the H2 and Ar matrixes shift this absorption to lower
wavenumbers. The analogous In2H2 species absorbs higher at
982.6 cm-1 in solid neon. Our B3LYP calculations predict Tl2D2
at 648.8 cm-1 in the harmonic approximation (H/D ratio:
1.410), and the lower 1.378 neon matrix isotopic frequency ratio
is due to anharmonicity in the vibration. Upon symmetry
lowering to Tl2HD, the normal mode changes and our B3LYP
Our B3LYP calculations predict the two TlH2 modes at 1530
and 1415 cm-1, which are 0.6 and 1.8% higher than the
hydrogen matrix values. On the other hand, our BPW91
computations find values of 1483 and 1354 cm-1, which are
2.4 and 2.6% lower than the observed values. These are the
comparisons expected for DFT frequencies.
calculation predicts the strongest Tl2HD mode at 832.0 cm-1
,
TlH3. Weak, sharp bands appear at 1748.4 (1254.4) cm-1
upon irradiation of solid H2 (D2) samples. With solid HD, these
bands shift to 1747.3 and 1258.1 cm-1, which are the effects
expected for TlH2D and TlHD2. Solid molecular hydrogens are
required for the product, as no counterparts were observed in
solid neon or argon.
83/266 of the way from the Tl2H2 to Tl2D2 frequencies. Our
observed Tl2HD band is 70/256 of the way from the neon matrix
Tl2H2 to Tl2D2 values.
Annealing increases sharp new bands at 1430.8 and 1424.3
cm-1 in H2 with a weaker 1020.5 cm-1 D2 counterpart: the
H/D ratio 1.396 is slightly higher than the values for the nearby
TlH2 absorptions. The growth upon annealing invites consid-
eration of another Tl2H2 isomer. Calculations for the Ga and In
analogues17,18,41 show that the C2V MMH2 isomer is next in
energy, but our DFT calculations find the Cs isomer next with
the C2V and C2h isomer energies within 6 kcal/mol. However,
the observed frequencies match best for the C2V TlTlH2 isomer
(Table 2). Annealing increases split bands at 1424.2 and 1423.0
cm-1 and at 1023.5 and 1022.6 cm-1 in pure HD that show the
small sretch-stretch interaction calculated for the TlTlH2
isomer. Our B3LYP calculation predicts close b2 and a1 modes,
and the 1430.8 and 1424.3 cm-1 bands are assigned accordingly.
Tl+(H2)n. The sharp bands at 4113.6 (2962.8) cm-1 (Figure
4) decrease upon full arc irradiation, never to return. An
intermediate 3596.3 cm-1 counterpart is observed with pure HD.
The former absorptions follow a series of like bands with Al
(4108.7 and 2959.4 cm-1), Ga (4108.9 and 2960.4 cm-1), and
In (4113.1 and 2961.9 cm-1) for the metal cation trapped in
the solid molecular hydrogen lattice and the resulting perturba-
tion on the solvating H2 (D2) ligand vibration. The small metal
dependence on this species arises from the weak interaction.
Our B3LYP calculation shows that the side-bound Tl+(H2)
B3LYP calculations found a trigonal planar TlH3 species with
a 1719 cm-1 antisymmetric mode and a 1.730 Å bond length.
Furthermore, our B3LYP calculations also find TlH2D to be
2.1 cm-1 lower than TlH3 and TlHD2 and 3.3 cm-1 higher than
TlD3, which is in excellent agreement with the observed -1.1
and +5.4 cm-1 observed isotopic shifts for these mixed isotopic
trihydrides. Relativistic MP2 calculations earlier predicted a
1.728 Å distance and a 1741 cm-1 frequency,26 and these higher
level calculations are closer to our experimental observation for
TlH3. On the basis of the neon matrix shift for the antisymmetric
mode for TlH2, we expect the gas-phase TlH3 fundamental to
be at 1760 ( 10 cm-1
.
Our TlH3 band absorbance is much less than what we
observed for InH3, which in turn is much less than what we
observed for GaH3 and AlH3, and is the expected trend.26
Evaporation of the H2 (D2) matrix gave no evidence of broad
absorption bands in the 1500-700 cm-1 region that might be
due to solid thallium hydride. The low yield of TlH3 and our
failure to observe (TlH3)n at low temperature probably is due
to the inherent instability of Tl(III) hydride, which casts doubt
on the claimed synthesis of (TlH3)n.39,40

3400 J. Phys. Chem. A, Vol. 108, No. 16, 2004
Wang and Andrews
TABLE 2: Calculated Structures and Vibrational Frequencies (cm-1) for Thallium Hydrides
structure:
bond length,
rel energy,
species
TlH (C∞V
state Å, or angle, deg kcal/mol
frequencies, cm-1 (sym, intensities, km/mol)
B3LYP/6-311++G(d,p)/LanL2DZ
TlH: 1236.4 (1206). TlD: 876.7 (606)
TlH2: 1355.6 (b2, 642), 1214.6 (a1, 231), 506.4 (a1, 95)
TlD2: 962.4 (324), 860.2 (117), 359.5 (48)
)
1Σ
TlH: 2.024
TlH: 1.929
HTlH: 120.2
TlH: 1.830
TlH2 (C2V)
2A1
TlH3 (D3h)
1A1′
TlH3: 1657.7 (a1′, 0), 1645.6 (e′, 498 × 2), 564.8 (a2′′, 200), 531.8 (e′, 229 × 2)
B3LYP/6-311++G(d,p)/SDD
TlH: 1306.0 (1159). TlD: 926.1 (583)
TlH2: 1530.8 (b2, 660), 1415.3 (a1, 178), 616.3 (a1, 133)
TlH (C∞V
TlH2 (C2V)
)
1Σ
TlH: 1.905
TlH: 1.787
HTlH: 121.9
TlH: 1.988
HTlH: 91.8
TlH: 3.126
HH: 0.747
TlH: 1.660
HTlH: 180.0
TlH: 1.730
HTlH: 120.0
2A1
0.0
-32.3
103
TlD2: 1086.9 (333), 1002.1 (90), 437.7 (67)
TlH2- (C2V)
1A1
TlH2-: 1029.6 (a1, 1880), 1019.4 (b2, 2016), 622.5 (a1, 78)
TlD2-: 730.2 (942), 722.9 (1009), 441.3 (37)
Tl+(H2) (C2V) 1A1
Tl+(H2): 4369.5 (a1, 52), 195.4 (b2, 17), 193.8 (a1, 13)
Tl+(D2): 3090.9 (26), 138.3 (8), 137.7 (7)
TlH2+ (D∞h
TlH3 (D3h)
)
1Σg
150
TlH2+: 2054.2 (σu, 15), 1961.7 (σg, 0), 713.7 (πu, 30 × 2)
+
TlD2+: 1460.1 (8), 1387.7 (0), 507.3 (16 × 2)
1A1′
TlH3: 1753.5 (a′, 0), 1718.8 (e′, 445 × 2), 666.6 (a2′′, 181), 614.1 (e′, 210 × 2)
TlD3: 1240.4 (0), 1219.5 (227 × 2), 475.0 (92), 436.2 (106 × 2)
TlH2D: 1742.2 (142), 1716.7 (463), 1229.6 (136), 612.6 (214), 609.5 (151), 503.0 (139)
TlHD2: 1728.7 (306), 1233.0 (84), 1222.8 (206), 559.8 (178), 546.4 (122), 436.5 (105)
TlH4-: 1536.0 (a1, 0), 1415.5 (t2, 956 × 3), 642.1 (e, 0 × 2), 608.0 (t2, 583 × 3)
TlD4-: 1086.6 (0), 1003.4 (483 × 3), 454.2 (0 × 2), 433.3 (288 × 3)
Tl2H2: 982.0 (ag, 0), 914.9 (b1u, 2435), 707.9 (b2u, 491), 664.1 (b3g, 0), 303.3 (b3u, 11), 95.0 (ag, 0)
Tl2HD: 891.7 (114), 832.0 (1714), 552.1 (255), 517.5 (116), 262.5 (8), 95 (0)
Tl2D2: 694.8 (0), 648.8 (1224), 502.0 (247), 470.3 (0), 215.1 (60), 95.0 (0)
Tl2H2: 1381.6 (a′, 1293), 1003.7 (a′, 506), 592.6 (a′, 674), 318.6 (a′, 5), 196.1 (a′′, 5), 50.7 (a′, 2)
TlH4- (Td)
Tl2H2 (D2h)
1A1
1Ag
TlH: 1.807
TlH: 2.157
HTlH: 109.9
0.0
Tl2H2 (Cs)
1A′
TlH: 1.845
TlH′: 2.340
TlTl′: 3.285
Tl′H′: 2.041
HTlH′: 99.2
TlH: 1.867
TlTl: 3.352
TlTlH:
TlH: 1.793
TlTl′: 3.129
HTlH: 107.9
TlH: 2.012
TlH′: 1.700
TlHTl: 100.7
H′TlH′: 137.1
12.4
Tl2H2 (C2h)
Tl2H2 (C2V)
Tl2H6 (D2h)
1Ag
1A1
1Ag
17.3
18.2
Tl2H2: 1358.0 (bu, 2193), 1350.7 (ag, 0), 333.6 (ag, 0), 130.9 (au, 48), 40.7 (ag, 0), 35.4 (bu, 14)
Tl2H2: 1508.4 (b2, 710), 1505.8 (a1, 1069), 642.7 (a1, 498), 315.1 (b1, 81), 160.8 (b2, 35), 87.6 (a1, 4)
Tl2H6: 1833.3 (b2u, 653), 1828.6 (ag,0), 1824.9 (b3u, 164), 1824.0 (b1g, 0),
1186.5 (ag, 0), 1078.2 (b3u, 1333), 1001.3 (b2g, 0), 914.3 (b1u, 460),
680.1 (b2u, 196), 648.9 (b3g, 0), 611.1 (ag, 0), 606.5 (b1u, 109), 503.8 (b3u, 972),
401.5 (b1g, 0), 368.8 (au, 0), 196.3 (b2u, 0), 134.3 (b2g, 0), 107.8 (ag, 0)
BPW91/6-311++G(d,p)/SDD
TlH: 1278.3 (1039). TlD: 906.4 (522)
TlH2: 1483.4 (b2, 605), 1353.9 (a1, 173), 591.3 (a1, 110)
TlD2: 1053.3 (305), 958.6 (87), 419.9 (55)
TlH2-: 1011.8 (a1, 1738), 1008.3 (b2, 1839), 594.1 (a1, 58)
TlD2-: 717.6 (870), 715.0 (920), 421.2 (27)
Tl+(H2): 4264.8 (a1, 83), 232.7 (a1, 20), 225.4 (b2, 18)
Tl+(D2): 3016.8 (41), 165.4 (11), 159.5 (9)
TlH2+: 1994.7 (eu, 9), 1883.8 (eg, 0), 708.5 (πu, 18 × 2)
TlH (C∞V
TlH2 (C2V)
)
1Σ
TlH: 1.923
TlH: 1.864
HTlH:
2A1
0.0
-31.1
103
TlH2- (C2V)
1A1
TlH: 2.006
HTlH: 91.4
TlH: 3.004
HH: 0.751
TlH: 1.674
HTlH: 180.0
TlH: 1.744
HTlH: 120.0
TlH: 1.818
TlH: 2.162
TlHTl: 109.5
TlH: 1.853
TlH′: 2.284
TlTl′: 3.179
HTlH′: 101.0
TlH: 1.870
TlTl: 3.199
HTlH: 121.8
TlH: 1.810
TlTl′: 3.122
HTlH: 107.2
TlH: 2.026
TlH′: 1.711
TlHTl: 100.1
H′TlH′: 138.3
Tl+(H2) (C2V) 1A1
TlH2+ (D∞h
TlH3 (D3h)
)
1Σg
151
1A1′
TlH3: 1685.1 (a1′, 0), 1668.4 (e′, 423 × 2), 647.1 (a2′′, 143), 583.6 (e′, 181)
TlH4- (Td)
Tl2H2 (D2h)
1A1
1Ag
TlH4-: 1479.6 (a1, 0), 1382.4 (t2, 927 × 3), 617.8 (e, 0 × 2), 578.8 (t2, 504 × 3)
Tl2H2: 957.1 (ag, 0), 922.3 (b1u, 2003), 739.3 (b3g, 0), 715.4 (b2u, 424), 291.3 (b3u, 11), 94.4 (ag, 0)
Tl2D2: 677.2 (0), 654.0 (1007), 523.6 (213), 206.5 (5), 94.4 (0)
0.0
Tl2H2 (Cs)
1A′
12.1
Tl2H2: 1358.3 (a′, 1103), 952.7 (a′, 409), 638.3 (a′, 531), 336.9 (a′, 0), 205.6 (a′′, 5), 66.6 (a′, 2)
Tl2H2 (C2h)
Tl2H2 (C2V)
Tl2H6 (D2h)
1Ag
1A1
1Ag
18.3
18.7
Tl2H2: 1333.4 (bu, 1861), 1323.3 (ag, 0), 363.0 (ag, 0), 146.1 (au, 45), 89.7 (bu, 18), 56.1 (ag, 0)
Tl2H2: 1459.1 (b2, 650), 1448.7 (a1, 939), 612.2 (a1, 396), 302.3 (b1, 66), 150.7 (b2, 30), 87.8 (a1, 3)
Tl2H6: 1787.6 (b2u, 598), 1777.1 (b1g, 0), 1765.4 (ag, 0), 1763.1 (b3u, 162), 1143.7 (ag, 0),
1040.8 (b3u, 1191), 985.3 (b2g, 0), 909.8 (b1u, 380), 635.7 (b2u, 151), 617.9 (b3g, 0),
586.1 (ag, 0), 585.6 (b1u, 82), 482.7 (b3u, 809), 391.2 (b1g, 0), 355.6 (au, 0), 210.0 (b2g, 0),
186.2 (b2u,0), 105.2 (ag,0)

Infrared Spectra of Thallium Hydrides
J. Phys. Chem. A, Vol. 108, No. 16, 2004 3401
TABLE 3: Group 13 Metal Hydride Stretching Frequencies Observed in Solid Hydrogena-c
M+(H2)n
(H2)MH3
4061.6
M2H6
MH3
1884
M2H5
M2H4
MH2
MMH2
MH4
1638
MH
MH2
M2H2
1156
(MH3)n
1720
-
-
Al
Ga
In
4108.7
1932
1915
1995
1976
1820
1803
1918
1845
1967
1838
1826
1875
1863
1707
1704
1822
1788
1815
1746
1629
1563
1520
1390
1599
(1430)
4108.9
4113.1
4113.6
4087.3
4098.5
1929
1761
1748
1783
1530
1424
1774
1608
1517
1393
1311
1356
1035
980
1900
1500
1460
(1225)
Tl
909
a References 14-18. b M+(H2)n and (H2)MH3 are sharp bands for H-H ligand stretching frequencies. The AlH2 value is calculated from the
AlD2- value in D2 times the AlH2/AlD2 frequency ratio. (MH3)n are solid film spectra. c The values for B+(H2)n, 4089.3 cm-1, and B+(D2)n, 2940.4
cm-1, are unpublished results from this laboratory.
-
structure is more stable than the linear (HTlH)+ structure, but
here we have a more highly coordinated Tl+ species that is
displaced 39.2 cm-1 below the 4152.8 cm-1 frequency for the
solid n-H2 lattice.46 Finally, charge balance is achieved in these
experiments by trapping H- (D-) in solid H2 (D2), as evidenced
by strong 3972 (2870) cm-1 absorptions.47
large and the Tl2H2, Tl2HD, and Tl2D2 yields from reaction 7
are statistical (Figure 6).
Tl2 + H2 UV8 Tl2H2
(5)
Tl + H f TlH
2TlH f Tl2H2
(6)
(7)
Emission Spectra. Two properties of the 193 nm induced
Tl emission spectra in solid H2 and D2 are interesting. In H2,
2
2
the two S1/2 f P1/2,3/2 components are blue-shifted 210 and
320 ( 20 cm-1, and in solid D2, these bands are blue-shifted
660 and 780 ( 20 cm-1. Not only has D2 blue-shifted the
emissions ∼450 cm-1 more than H2, but also the spin-orbit
splitting (7793 cm-1 in the gas phase) has decreased by 120 (
10 cm-1 in solid D2 and by 110 ( 10 cm-1 in solid H2. The
smaller lattice parameter (3.600 Å) for solid n-D2 suggests a
more repulsive cage interaction than that for solid n-H2 (3.769
Å).48,49 Spin-orbit splitting is often diminished in the matrix,50
and these small decreases (1.4-1.9%) are reasonable. Finally,
the emission yield for Tl was much higher than that found for
In and Ga in solid hydrogen, which attests the lower reactivity
of Tl with H2.
Reaction Mechanisms. The reactions of Tl and H2 observed
here are common to those for the other group 13 metals. The
initial reaction (eq 1) is endothermic (∆E ) 58 kcal/mol)1 and
must be driven by exciting the metal atom. The insertion reaction
(eq 2) also requires activation energy. Note that λ > 240 nm
irradiation (Figure 1b) markedly increases the yield of both TlH
and TlH2 and produces TlH3 from reactions 3 and 4.
Annealing in solid hydrogen fosters the further reaction of
Tl with TlH2, as reactions 1-3 require activation energy.
Tl + TlH2 f TlTlH2
(8)
The laser-ablation process produces metal cations as well as
neutral atoms,51 as seen from the emission spectrum (Figure
7), and the Tl+ cation complex is formed upon trapping of Tl+
in solid H2.
Tl+ + nH2 f Tl+(H2)n
(9)
Conclusions
Laser-ablated Tl atoms react with H2 much the same as In,
Ga, and Al, but major differences do exist. Thallium is less
reactive: The lower product band and higher 193 nm atomic
emission yield attest this fact. The dominant thallium product
is Tl(I)H, whereas the major aluminum product is Al(III)H3.
This substantiates the observation of Al2H6 and solid (AlH3)n
and the absence of Tl2H6 and solid (TlH3)n in the product
spectrum. Although the yield of TlH3 is small, its identification
with TlH2D, TlHD2, and TlD3 isotopic modifications is defini-
tive. Table 3 summarizes the group 13 metal hydride stretching
frequencies: The TlH3 fundamental is only 13 cm-1 below the
InH3 value, whereas the TlH2 and TlH modes are 173-82 cm-1
below their indium counterparts.
The reaction of metal dimer M2 with H2 gives the rhombic
M2H2 dimer, although the reactions are spontaneous for Al2 and
Ga2 but they require photochemical activation for In2 and Tl2.
A significant yield of the TlTlH2 isomer is also observed. Sharp
2S1/2 f 2P1/2,3/2 emission from unreacted atomic Tl induced by
193 nm radiation is blue-shifted 660 cm-1 in solid D2 and 210
cm-1 in solid H2.
Tl + H2 f TlH + H
Tl + H2 f TlH2
(1)
(2)
TlH + H2 f TlH3
TlH2 + H f TlH3
(3)
(4)
Unreacted Tl clusters form Tl2, and this reaction is favored
in the soft neon matrix. Then irradiation leads directly to Tl2H2
formation (reaction 5). Such is the mechanism proposed for
In2H2, but the reactions with Al2 and Ga2 are spontaneous. Note
the experiments with HD in neon gave major Tl2HD and those
with H2 + D2 in neon favored Tl2H2 and Tl2D2 (Figure 5), which
confirms the reduction in reaction 5. Very similar results are
observed in solid argon (Figure 6). In the more rigid argon
matrix at 3.5 K, unreacted Tl is isolated and H atoms from
dissociation by laser plume radiation react upon annealing to
form TlH, which also can dimerize (reactions 6 and 7). With
higher laser energy, the yields of TlH and TlD from HD are
Although the DFT calculated electron affinity for TlH2 is 32
-
kcal/mol, we have no definitive evidence for the TlH2 anion
in the spectrum. This may arise from detachment by irradiation
-
in the experiment. On the other hand, AlH4 is the dominant
anion observed with Al.
The group 13 metal cations all form weak complexes with
H2 in the solid lattice with a H-H stretching mode 39-44 cm-1
below the solid H2 fundamental at 4153 cm-1
.

3402 J. Phys. Chem. A, Vol. 108, No. 16, 2004
Wang and Andrews
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Density functional theory using the relativistic SDD pseudo-
potential is adequate to calculate frequencies for thallium
hydrides, but these calculations fit better for TlH > TlH2 >
TlH3. However, relativistic MP2 calculations produce more
accurate frequencies for TlH3. It must be noted that the
LANL2DZ pseudopotential and basis is vastly inferior for
thallium hydrides.
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Acknowledgment. We gratefully acknowledge support for
this work from NSF Grant CHE 00-78836.
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