Electronic properties of CrF and CrCI in the X6∑+ state: Observation of the halogen hyperfine structure by Fourier transform microwave spectroscopy

Article abstract of DOI:10.1063/1.1691021

The rotational spectra of the CrF and CrCl radicals in the X ⁶σ⁺ was discussed. It was stated that the CrF and CrCl radicals were generated by the reaction of laser-ablated Cr with F ₂ and Cl₂, respectively dilu

Full text of DOI:10.1063/1.1691021

Electronic properties of CrF and CrCl in the X 6 Σ + state: Observation of the halogen
hyperfine structure by Fourier transform microwave spectroscopy
Kaoru Katoh, Toshiaki Okabayashi, Mitsutoshi Tanimoto, Yoshihiro Sumiyoshi, and Yasuki Endo
Citation: The Journal of Chemical Physics 120, 7927 (2004); doi: 10.1063/1.1691021
View online: http://dx.doi.org/10.1063/1.1691021
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JOURNAL OF CHEMICAL PHYSICS
VOLUME 120, NUMBER 17
1 MAY 2004
6
Electronic properties of CrF and CrCl in the X ⌺¿ state:
Observation of the halogen hyperfine structure by Fourier
transform microwave spectroscopy
Kaoru Katoh,a) Toshiaki Okabayashi,b) and Mitsutoshi Tanimoto
Department of Chemistry, Faculty of Science, Shizuoka University, 836 Oya, Shizuoka 422-8529, Japan
Yoshihiro Sumiyoshi and Yasuki Endo
Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo, Komaba,
Meguro-ku, Tokyo 153-8902, Japan
͑Received 23 January 2004; accepted 9 February 2004͒
The rotational spectra of the CrF and CrCl radicals in the X 6⌺ϩ state were observed by employing
a Fourier transform microwave spectrometer. The CrF and CrCl radicals were generated by the
reaction of laser-ablated Cr with F2 and Cl2 , respectively, diluted in Ar. A chromium rod made of
chromium powder pasted with epoxy resin was ablated by a Nd:YAG laser. Rotational transitions
were measured in the region between 8 and 26 GHz. Several hyperfine constants due to the halogen
nuclei were determined by a least-squares analysis. The electronic properties of CrF and CrCl were
derived from their hyperfine constants and were compared with those of other 3d transition metal
monohalides: TiF, MnF, FeF, CoF, NiF, and FeCl. © 2004 American Institute of Physics.
͓DOI: 10.1063/1.1691021͔
A 6⌺ϩ –X 6⌺ϩ transition with high resolution and carried
out a rotational analysis.1,2 Devore et al.3 studied chemilumi-
nescence of CrF and obtained low-resolution spectra of sev-
eral electronic bands. Launila and his associates4,5 reported a
high resolution Fourier transform spectrum of the A–X
band. Subsequently, they observed the B 6⌸–X 6⌺ϩ band as
well as the A 6⌺ϩ –X 6⌺ϩ band of CrF.6 Pure rotational tran-
sitions of CrF were observed by Okabayashi and Tanimoto7
in the discharge plasma of CF4 diluted in He with chromium
powder laid on an electrode plate.
For CrCl, the first reliable low-resolution electronic
spectrum was observed by Rao and Rao.8 More lately, Oike
et al. detected the pure rotational spectrum of CrCl in the
discharge plasma of AlCl3 diluted in He using stainless steel
electrodes.9,10 Launila and his co-workers observed a high
resolution Fourier transform spectrum of the A 6⌺ϩ –X 6⌺ϩ
and B 6⌸–X 6⌺ϩ bands of CrCl.11,12 Several theoretical cal-
culations were also published for CrF and CrCl in the ground
and low-lying electronic excited states.11–13
Observation of the hyperfine structure is a powerful
method to study the electronic property in the electronic state
concerned,14 because the hyperfine interaction is quite sensi-
tive to the environment where valence electrons move. Metal
monohalides, however, are generally so ionic that their hy-
perfine splittings due to the halogen nuclei are often too
small to be observed with a conventional millimeter-wave
spectrometer. Indeed, the previous millimeter-wave studies
on CrF and CrCl ͑Refs. 7, 9, 10͒ did not observe their hy-
perfine structures. In the present paper, we report results ob-
tained by Fourier transform microwave ͑FTMW͒ spectros-
copy, which is higher-resolution method than a conventional
millimeter-wave spectroscopy, on the CrF and CrCl radicals
generated by the laser-ablation technique. Their electronic
properties have been determined from the hyperfine con-
I. INTRODUCTION
Transition metal compounds often have high electron-
orbital and electron-spin angular momenta due to their
d-electrons. The d-electrons cause a lot of low lying elec-
tronically excited states. Existence of such electronic states
and their substates results in remarkably complex spectra to
be observed by high resolution spectroscopic methods. It is
quite complicated to analyze them and to understand the
physical significance of spectroscopic constants. Since it is
difficult to produce the transition metal compounds effi-
ciently in the gas phase, high sensitivity spectrometers have
been employed to study electronic spectra of such species.
Moreover, most of the works carried out so far have been
those of hydrides and oxides. Only a few works have been
reported for other species like halides, nitrides, carbides, etc.
The diatomic transition metal halides MX (M
ϭtransition metal; XϭF, Cl, Br, and I͒ are highly ionic spe-
cies represented as MϩXϪ. All unpaired electrons mainly
exist on the metal atom because of the closed shell structure
of the XϪ ion. Thus their electronic states strongly reflect the
character of the metallic ion, Mϩ. It is interesting to compare
electronic structures of MF, MCl, MBr, and MI, but there
were only a limited number of works except for the ⌺ϩ
species like CuX and AgX until several years ago.
Chromium monohalides (CrX) are the species that have
scarcely been studied by any spectroscopic methods. Re-
cently the electronic spectra of CrF and CrCl have been stud-
ied by a few groups. The first spectroscopic study on CrF
was reported by Dubov et al., who observed the
1
a͒
Present address: Department of Basic Science, Graduate School of Arts
and Sciences, The University of Tokyo, Komaba, Meguro-ku, Tokyo
153-8902, Japan.
b͒
Electronic mail: sctokab@ipc.shizuoka.ac.jp
0021-9606/2004/120(17)/7927/6/$22.00
7927
© 2004 American Institute of Physics
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7928
J. Chem. Phys., Vol. 120, No. 17, 1 May 2004
Katoh et al.
FIG. 3. Observed Nϭ1Ϫ0, Jϭ3.5Ϫ2.5, Fϭ4Ϫ3 transition of CrF gener-
ated by the reaction of laser-ablated Cr with 0.1% F2 and 2% He diluted in
Ar ͑a͒ without discharge and ͑b͒ with discharge. Each spectrum is obtained
after 200 shots of accumulation.
FIG. 1. Schematic diagrams of ͑a͒ a normal laser-ablation nozzle for CrCl
generation and ͑b͒ a laser-ablation nozzle with pulsed discharge for CrF
generation.
For the CrF generation, 0.1% F2 and 2% He diluted with
Ar was used as a precursor of fluorine. However, the ablation
system mentioned above did not give strong signal of CrF.
When F2 gas was replaced by CF4 gas, the CrF signal was
not observed at all. In order to improve the signal strength of
CrF, we adopted another type of an ablation nozzle with
simultaneous electrical discharge17 shown in Fig. 1͑b͒. This
combined production system provided about three times
stronger signal of CrF than the conventional laser ablation
system as shown in Fig. 3. The timing chart of the FTMW
spectrometer is given in Fig. 4. The line strength of CrF is
insensitive to the change in laser-shot timing with respect to
the pulsed discharge. Using this system, CF4 gas as well as
F2 gas gave the CrF signal, but the latter gave much stronger
signal. In total, three lines of CrF were observed in the re-
gion between 22 and 26 GHz.
stants and discussed through a comparison with those of
other metal monohalides.
II. EXPERIMENT
The present experiment was carried out using a Fourier
transform microwave spectrometer with a laser-ablation sys-
tem at University of Tokyo.15,16 The CrCl radical was gener-
ated in an adiabatic expansion of laser-vaporized Cr with an
Ar stream containing about 0.1% of Cl2 with a conventional
laser ablation nozzle source illustrated in Fig. 1͑a͒. A chro-
mium target rod was formed from chromium powder pasted
with epoxy resin. As a power source of vaporization, the
second harmonic ͑532 nm͒ of a Nd:YAG laser was employed
with 40 mJ/pulse. Using this system, the CrCl signals were
strong enough to be observed easily. A typical observed spec-
trum is illustrated in Fig. 2. When Cl2 gas was replaced by
CCl4 vapor, the CrCl signal was also observed but was
somewhat weaker. In total, 25 lines of CrCl were observed in
the region between 9 and 20 GHz.
FIG. 2. Observed Nϭ2Ϫ1, Jϭ4.5Ϫ3.5 transition with the 37Cl hyperfine
structure of Cr37Cl, which is generated by the reaction of laser-ablated Cr
with 0.1% Cl2 diluted in Ar without discharge. The spectrum is obtained
after 240 shots of accumulation.
FIG. 4. Timing chart of the FTMW spectrometer with both laser ablation
and electrical discharge.
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J. Chem. Phys., Vol. 120, No. 17, 1 May 2004
Electronic properties of CrF and CrCl
7929
states.a
TABLE III. Observed transition frequencies of CrCl in MHz.
6
ϩ
TABLE I. Molecular constants of CrF and CrCl in the X
⌺
CrF
Cr35Cl
Cr37Cl
Cr35Cl
Obs. Freq.
Cr37Cl
Obs. Freq.
B0
D0
H0
␭
11369.61702͑48͒
15.06022͑76͒
Ϫ7.70b
16157.49͑25͒
Ϫ15.500͑44͒
408.557͑10͒
Ϫ0.788͑10͒
Ϫ8.06͑72͒
Ϫ4.80͑27͒
20.5͑32͒
5009.34629͑76͒
3.52879͑68͒
0.0b
7989.429͑79͒
Ϫ13.270͑50͒
65.5799͑44͒
Ϫ0.1296͑33͒
Ϫ4.06͑70͒
Ϫ3.245͑10͒
Ϫ2.6710͑52͒
Ϫ6.717͑25͒
Ϫ17.401͑28͒
4847.85171͑75͒
3.30602͑63͒
0.0b
7990.290͑73͒
Ϫ12.776͑57͒
63.4714͑45͒
Ϫ0.1261͑33͒
Ϫ4.85͑82͒
Ϫ3.2528͑97͒
Ϫ2.2237͑39͒
Ϫ5.585͑18͒
Ϫ13.748͑20͒
MHz
kHz
mHz
MHz
kHz
MHz
kHz
kHz
MHz
MHz
MHz
MHz
N –N
Ј
J –J
Ј
F –F
Ј Љ
OϪCa
OϪCa
Љ
Љ
1–0 3.5–2.5 2.0–1.0 9776.6689
1–0 3.5–2.5 3.0–2.0 9776.2031
1–0 3.5–2.5 3.0–3.0
1–0 3.5–2.5 4.0–3.0 9776.8345
1–0 3.5–2.5 5.0–4.0 9777.8688 Ϫ0.0065 9517.4953 Ϫ0.0012
0.0051 9516.5201
0.0004 9516.1605
9520.0175 Ϫ0.0035
0.0011 9516.6666 0.0007
0.0016
0.0038
␭
D
␥
␥
D
2–1 0.5–1.5 1.0–1.0 11079.4766
2–1 0.5–1.5 1.0–2.0 11085.0263
0.0018 10544.8231 Ϫ0.0036
0.0023 10549.3519 0.0031
␥
S
␪
bF
c
2–1 0.5–1.5 2.0–2.0 11078.5297 Ϫ0.0007 10543.9359 Ϫ0.0002
2–1 0.5–1.5 2.0–3.0 11081.1719 Ϫ0.0034 10546.1688 0.0006
2–1 4.5–3.5 3.0–2.0 19931.1515 Ϫ0.0079 19323.7664 Ϫ0.0009
2–1 4.5–3.5 4.0–3.0 19930.9807 0.0085 19323.6201 Ϫ0.0016
2–1 4.5–3.5 5.0–4.0 19931.4387 Ϫ0.0036 19324.0005 0.0019
0.0030 19324.5066 Ϫ0.0014
Ϫ51.49͑78͒
¯
eQq
aValues in parentheses are one standard deviation.
bFixed in the analysis.
2–1 4.5–3.5 6.0–5.0 19932.0832
aObserved minus Calculated frequency.
III. ANALYSIS
The observed transition frequencies were analyzed by a
least-squares analysis for ⌺ states using a case (b)␤J cou-
pling scheme.14 The Hamiltonian employed is
dard errors. This was because the hyperfine constants were
indirectly restricted by the millimeter-wave data through the
simultaneous least squares determination of the hyperfine
and other constants.
HeffϭHrotϩHssϩHsrϩHhf ,
͑1͒
where Hrot represents the rotational energy including the cen-
trifugal distortion, Hss the spin–spin interaction, Hsr the
spin–rotation interaction, and Hhf the hyperfine interaction.
In order to fit the data within experimental error, two extra
higher order terms which do not appear in the electronic
states of triplet or lower multiplicity were needed: the third
order spin-rotation coupling term ␥S and the fourth order
spin–orbit coupling term ␪.18,19 As in Ref. 19, the basis set
was truncated in the calculations at ⌬NϭϮ4 without loss in
accuracy. Other matrix elements including the hyperfine in-
teractions were cited from Ref. 14. The molecular constants
were determined by a least squares calculation. In order to
determine the molecular constants accurately, the least
squares calculation was simultaneously carried out for the
combined millimeter-wave7,9,10 and the present FTMW data.
The FTMW data were subjected to the analysis with 100
times larger weights than the millimeter-wave data. The stan-
dard deviation of the fit was about 20 kHz for each species.
The molecular constants determined are listed in Table I. The
observed microwave frequencies and the residuals of the fit
are summarized in Table II for CrF and Table III for CrCl.
The residuals for CrF in Table II are zero for all the FTMW
measurements, because two independent hyperfine param-
eters bF and c were determined from three transition fre-
quencies observed. However, even if the experimental errors
were taken into account, the molecular constants determined
by the least squares fit were affected only within their stan-
IV. RESULTS AND DISCUSSION
Hyperfine splittings arising from the nuclear spin of
fluorine and chlorine were observed for CrF and CrCl, re-
spectively. The hyperfine parameters of Frosch and Foley,20
a, bF and c, are represented as
1
1
aϭ2␮BgN␮
l
,
͑2͒
͑3͒
͚
N
iz
ri3
ͳ ʹ
⌳
i
o
8␲
1
2
bFϭ
gs␮BgN␮
͉
⌿ 0͒
͑
͉
,
͘
s
͗
͚
N
i
3
n
i
and
3
1
3 cos2 ␪iϪ1
cϭ gs␮BgN␮
,
͑4͒
͚
N
ri3
ͳ
ʹ
2
n
i
s
where n refers to the number of unpaired electrons. In the
present study, however, the Frosch and Foley a hyperfine
parameter was not determined because the a constant is
meaningless in the ⌺ electronic state without an electronic
orbital angular momentum.
The electron configuration of CrF is supposed to be
(core)(9␴)1(1␦)2(4␲)2, and the unpaired electrons belong
to the 9␴, 1␦, and 4␲ orbitals. The 1␦ orbital is essentially
the 3d(Cr) orbital. The 4␲ orbital is mainly constructed
from the 3d(Cr) orbital but includes small amounts of the
4p(Cr) and 2p(F) orbitals. The 9␴ and 10␴ orbitals mainly
consist of the 4s(Cr) and 3d(Cr) orbitals, respectively, but
includes small amounts of the 2s(F) and 2p(F) orbitals.
Thus, the hyperfine constant bF is associated with the 2s(F)
orbital included in the 9␴ orbital. Similarly, the parameter c
represents the contribution of the 2p(F) orbitals to the 9␴
and 4␲ orbitals.
TABLE II. Observed transition frequencies of CrF in MHz.
N –N
Ј
J –J
Ј
F –F
Ј Љ
Obs. Freq.
OϪCa
Љ
Љ
1–0
1–0
2–1
3.5–2.5
3.5–2.5
0.5–1.5
3.0–2.0
4.0–3.0
1.0–2.0
22471.6995
22473.7032
25745.3591
0.000
0.000
0.000
The bF(F) and c(F) constants of CrF are related to the
atomic constants A(F)ϭ52870 and P(F)ϭ4400 MHz, re-
aObserved minus calculated frequency.
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7930
J. Chem. Phys., Vol. 120, No. 17, 1 May 2004
Katoh et al.
TABLE IV. Contributions of the 2p and 2s orbitals of fluorine to the 4␲,
9␴, and 10␴ orbitals of the fourth-row metal monofluorides in %.a
spectively, listed in Ref. 21. These hyperfine parameters are
thus simplified to the following approximate equations:
F(2p)
4␲
F(2p)
9␴
F(2p)
10␴
F(2s)
9␴
F(2s)
c
10␴
Ref.
c
c
c
c
8␲
1
5
2
bF F͒ϭ
gs␮BgN␮
͉⌿ 0͉͒
͓ ͑
͗ ͘
9␴
͑
2
ϩ
N
CaF
TiF
⌺
¯
0.80
¯
¯
0.23
¯
¯
¯
22
23
3
4
⌽
ϩ
4.6͑1͒ 0.7͑8͒
0.23͑8͒
0.19͑9͒
2
2
6
7
b
b
CrF
MnF
FeF
CoF
NiF
⌺
⌺
͓5.6͔
͓0.7͔
¯
This work
ϩ2 ⌿ 0͒
ϩ2 ͉⌿ 0͉͒
͑
͗ ͘
1␦
͓
͑
͔
͔
͗
͘
4␲
ϩ
c
c
c
d
d
͓5͔
͓5͔
͓1͔
͓7͔
͓9͔
͓0.2͔
͓0.6͔
͓0.7͔
¯
24
25
26
27
6
e
e
e
f
f
8␲
1
5
⌬
͓1͔
͓0.2͔
cF͑2s͒
͉
⌿ 0͒
͉
2
3
ϭ
gs␮BgN␮
͓
͑
͔
͗
͘
2s␴͑F͒
⌽
6.6
4.5͑3͒
¯
¯
¯
N
9␴
4
3
2
⌸
¯
¯
¯
¯
3/2
F͑2a͒
9␴
c
aNumbers in parentheses in the table and footnotes b–f represent three stan-
Ӎ
A F͒,
͑
͑5͒
ͫ
ͬ
dard deviations. Errors for CaF and CoF are small enough.
5
bAssumed value to reproduce c4F(␲2p)Ϫc
ϭ4.9(2). See text.
F(2p)
9␴
cAssumed value to reproduce Ϫc4F(␲2p)ϩc
ϩc
ϭ2.7(assumed).
F(2p)
F(2p)
10␴
and
9␴
dAssumed value to reproduce c9F(␴2s)ϩc
ϭ0.79.
F(2s)
10␴
3 cos2 ␪Ϫ1
F(2p)
9␴
F(2p)
eAssumed value to reproduce Ϫc4F(␲2p)ϩc
ϩc
10␴
ϭ4.9(3).
3
1
F(2s)
c F͒ϭ gs␮BgN␮
͑
ͳ
ʹ
N
r3
ͫ
fAssumed value to reproduce c9F(␴2s)ϩc
ϭ0.87(3).
10␴
2
5
9␴
3 cos2 ␪Ϫ1
3 cos2 ␪Ϫ1
ϩ2
ϩ2
ͳ
ʹ ͳ
ʹ
r3
r3
ͬ
1␦
4␲
these three species are primarily constructed from the 4s(M)
orbital, it is appropriate to assume that CaF, TiF, and CrF
3
3 cos2 ␪Ϫ1
F(2s)
9␴
F͑2p͒
9␴
have similar c
values. Under this assumption, CaF, TiF,
ϭ
gs␮BgN␮
c
ͳ
ʹ
N
r3
ͫ
10
F(2p)
9␴
2p␴͑F͒
and CrF have possibly similar c
efficient for CaF, 0.80%, is very close to that of TiF, 0.7͑8͒%,
values. Indeed, the co-
3 cos2 ␪Ϫ1
F͑2p͒
4␲
ϩ2c
even though the experimental error of the latter is large. If
ͳ
ʹ
r3
ͬ
F(2p)
9␴
F(2p)
value of CrF is assumed to be 0.7%, the c
4␲
2p␲͑F͒
the c
value is obtained to be 5.6%, which is a reasonable value in
comparison with those of other metal monofluorides ͑about
5%͒.
6
Ӎ
cF͑2p͒ϪcF͑2p͒ P F͒,
͑6͒
͓
͔ ͑
9␴
4␲
25
For MnF (core)(9␴)1(1␦)2(4␲)2(10␴)1 and FeF
F(2s)
9␴
͓
͔
where c
shows 2s(F) character in the 9␴ orbital. The
(core)(9␴)1(1␦)3(4␲)2(10␴)1 , there is a more serious
F(2p)
4␲
F(2p)
represent the contributions of
9␴
͓
͔
coefficients c
and c
problem in the analysis of the hyperfine interaction. In an
early 3d transition metal fluoride like TiF, the 9␴ and 10␴
orbitals have dominant contributions of the 4s(M) and
3d␴(M) orbitals, respectively. However, in a late 3d transi-
tion metal monofluoride like NiF, the 4s(M) and 3d␴(M)
orbitals strongly mix to form the hybrid 9␴ and 10␴ orbitals.
For MnF and FeF, the 9␴ orbitals are still mainly constructed
from the 4s(M) orbitals, but include certain amounts of the
3d␴(M) orbitals. It is very difficult to separate out the con-
tribution of the hybridization to the observed hyperfine con-
the 2p(F) orbitals to the 4␲ and 9␴ orbitals, respectively.
The angular factor 3 cos2 ␪Ϫ1
and 3 cos2 ␪Ϫ1
͘
are
͗
͘
͗
2p␲
2p␴
taken to be Ϫ2/5 and 4/5, respectively.21 In order to repro-
duce the observed value bF(F)ϭ20.5 MHz, we obtained
F(2s)
9␴
F(2p)
4␲
F(2p)
value was de-
9␴
c
ϭ0.19%. Similarly, the c
Ϫc
rived to be 4.9% from c(F)ϭϪ51.49 MHz. These values are
consistent with the conjecture that the 4␲ and 9␴ orbitals are
predominantly formed from the Cr atomic orbitals. This
means that the fluorine atom exists almost as a closed shell
FϪ ion and is hardly associated with unpaired electrons.
Recently, there are several reports on hyperfine interac-
tions for the fourth-row metal monofluoride radicals bearing
unpaired electrons. Hyperfine analysis similar to that per-
formed in the preceding paragraph was also carried out for
several monofluorides to estimate the contributions of fluo-
rine atomic orbitals to the relevant molecular orbitals. The
F(2p)
9␴
F(2p)
values of MnF and FeF
10␴
stants. Since the c
and c
depend strongly on the hybridization, we cannot estimate the
F(2p)
9␴
F(2p)
values separately. In the present analysis we
10␴
c
and c
F(2p)
thus assume that the c
values of MnF and FeF have
9␴
slightly larger value ͑1%͒ than those of early 3d transition
metal fluorides, although the uncertainties attached are large.
F(2p)
10␴
Under this assumption, the c
values of MnF and FeF are
results are summarized in Table IV. It is interesting that the
F(2p)
estimated to be 7% and 9%, respectively. These values are
c
͓
value of an early 3d transition metal monofluoride TiF
4␲
F(2p)
9␴
(core)(9␴)1(1␦)1(4␲)1 is very close to those of late 3d
much larger than the c
values ͑about 1%͒. This means
͔
transition metal fluorides CoF (core)(9␴)2(1␦)3(4␲)3
that the 2p␴(F) orbital interacts more strongly with the
3d␴(M) orbital than with the 4s(M) orbital. This finding
probably reflects that the 3d␴(M) orbital extends more
widely along the molecular axis than the 4s(M) orbital.
͓
͔
and NiF (core)(9␴)2(1␦)4(4␲)3 . The 4␲ orbitals of these
͓
͔
three species are mainly composed of the 3d␲(M) orbitals
of the metals and partially of the 2p␲(F) orbital of fluorine.
F(2s)
9␴
F(2s)
.
10␴
A similar analysis was carried out for c
and c
This hybrid scheme also applies to the other fluorides ͑CrF,
F(2s)
F(2p)
4␲
If c
of MnF and FeF are similar to those of early 3d
MnF, and FeF͒ in Table IV. Thus, their c
values may
9␴
F(2s)
10␴
reasonably be estimated to be about 5%.
transition metal monofluorides ͑0.2%͒, the c
values are
F(2s)
9␴
The c
values of CaF (core)(9␴)1 , TiF, and CrF
obtained to be 0.6% and 0.7% for MnF and FeF, respectively.
͓ ͔
F(2s)
9␴
have similar values of about 0.2%. Since the 9␴ orbitals of
These values are apparently larger than the assumed c
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J. Chem. Phys., Vol. 120, No. 17, 1 May 2004
Electronic properties of CrF and CrCl
7931
TABLE V. Contributions of the 3p and 3s orbitals of chlorine to the 5␲,
11␴, and 12␴ orbitals of the fourth-row metal monochlorides in %.a
Cl(3p)
5␲
Cl(3p)
11␴
Cl(3p)
12␴
Cl(3s)
11␴
Cl(3s)
c
12␴
Ref.
c
c
c
c
2
6
ϩ
ϩ
CaCl
CrCl
FeCl
⌺
⌺
¯
2.4
¯
0.41
¯
30
This work
32
b
b
͓8͔
͓2͔
¯
Ϫ0.23c
¯
6
d
d
d
e
e
⌬
͓8͔
͓2͔
͓11͔
͓0.4͔
͓0.4͔
aValues in parentheses in footnotes b–e represent three standard deviations.
Errors for CaCl values are small enough.
Cl(3p)
bAssumed value to reproduce c5C␲l(3p)Ϫc
ϭ6.4(1). See text.
11␴
cNegative c1C1l(␴3s) value is an effective one affected by the spin-polarization.
Cl(3p)
11␴
Cl(3p)
ϭ4.6(44).
12␴
dAssumed value to reproduce Ϫc5C␲l(3p)ϩc
ϩc
FIG. 5. The eQq(35Cl) values of the fourth-row element monochlorides in
MHz. The values are cited from Refs. 29–35. Experimental errors of the
species except for FeCl are small enough.
Cl(3s)
eAssumed value to reproduce cC11l(␴3s)ϩc
ϭ0.78(42).
12␴
values. Probably, this is also explained by the extended na-
ture of the 3d␴(M) orbital along the molecular axis as men-
tioned above.
constant is a molecular property and affected by the distribu-
tions of core- as well as valence-electrons, it is difficult to
discuss the constants more quantitatively without the help of
a high-level ab initio calculation when the orbital polariza-
tion is striking. The understanding of these hyperfine con-
stants including eQq(Cl) should be a good subject of current
theoretical calculations.
For CrCl (core)(11␴)1(1␦)2(5␲)2 , a similar analysis
͓
͔
Cl(3s)
11␴
Cl(3p)
5␲
was carried out to obtain c
ϭϪ0.23% and c
Cl(3p)
Ϫc
ϭ6.4(3)% from the observed bF(Cl) and c(Cl)
11␴
values and the atomic chlorine constants of A(35Cl)ϭ5723
and P(35Cl)ϭ439.0 MHz.21 It is impossible to explain the
Cl(3s)
negative c
value using Eq. ͑3͒. Such anomaly is often
11␴
accounted for by the contribution of the spin polarization.28
Table V summarizes the contributions of various chlorine
atomic orbitals in the fourth-row metal monochlorides. Since
studies on such metal monochlorides are limited, it is very
difficult to discuss their electronic properties systematically.
ACKNOWLEDGMENT
The research was partially supported by the Japan Soci-
ety for the Promotion of Science through Grant-in-Aid for
Scientific Research ͑No. 12740316͒.
However, by the analogy with metal monofluorides, it is
Cl(3s)
11␴
likely that the c
value of CaCl (core)(11␴)1 can
͓ ͔
be used in the analysis of CrCl. Under this assumption,
Cl(3p)
1 V. M. Dubov and E. A. Shenyavskaya, Opt. Spektrosk. 62, 195 ͑1987͒.
the c
value of CrCl is estimated to be about 8%. Sim-
5␲
2
´
V. M. Dubov, D. V. Tschechovskoy, E. A. Shenyavskaya, and I. Kovacs,
ilarly, the electronic properties of FeCl (core)
͓
(11␴)1(1␦)3(5␲)2(12␴)1] assumed to reproduce hyperfine
parameters are shown in Table V, but they suffer from con-
siderable uncertainties originating from the poor experimen-
tal accuracy. Even if such uncertainties are considered, each
parameter in Table V is systematically larger than the corre-
sponding value of the metal monofluoride in Table IV. This
probably reflects the fact that metal monochlorides are less
ionic and more covalent than the corresponding monofluo-
rides, contrary to the qualitative comparison between FeF
and FeCl in Ref. 32.
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7932
J. Chem. Phys., Vol. 120, No. 17, 1 May 2004
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