Fourier transform infrared emission spectroscopy of VCI

Article abstract of DOI:10.1063/1.1349426

The observation of a new electronic transition of VCl was reported in the 6000-8000 cm^-1 region using Fourier transform infrared emission spectroscopy technique. A rotational analysis of the 0-0 and 0-1 bands of the ⁵δ₁-⁵δ₁, ⁵δ₂-⁵δ₂, and ⁵δ₃-⁵δ₃ subbands were obtained. The rotational analysis of the remaining two subbands was not obtained due to severe overlapping from neighboring subbands.

Full text of DOI:10.1063/1.1349426

Fourier transform infrared emission spectroscopy of VCl
R. S. Ram, P. F. Bernath, and S. P. Davis
Citation: The Journal of Chemical Physics 114, 4457 (2001); doi: 10.1063/1.1349426
View online: http://dx.doi.org/10.1063/1.1349426
View Table of Contents: http://scitation.aip.org/content/aip/journal/jcp/114/10?ver=pdfcov
Published by the AIP Publishing
Articles you may be interested in
Reaction dynamics of O(1D) + HCOOD/DCOOH investigated with time-resolved Fourier-transform infrared
emission spectroscopy
J. Chem. Phys. 141, 154313 (2014); 10.1063/1.4897418
Photodissociation of CH3CHO at 248 nm by time-resolved Fourier-transform infrared emission spectroscopy:
Verification of roaming and triple fragmentation
J. Chem. Phys. 140, 064313 (2014); 10.1063/1.4862266
Infrared absorption of gaseous ClCS detected with time-resolved Fourier-transform spectroscopy
J. Chem. Phys. 126, 174310 (2007); 10.1063/1.2730501
Fourier transform infrared emission spectra of MgH and MgD
J. Chem. Phys. 120, 10002 (2004); 10.1063/1.1724821
Detection of ClSO with time-resolved Fourier-transform infrared absorption spectroscopy
J. Chem. Phys. 120, 3179 (2004); 10.1063/1.1641007
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 147.143.2.5
On: Sun, 21 Dec 2014 18:09:34

JOURNAL OF CHEMICAL PHYSICS
VOLUME 114, NUMBER 10
8 MARCH 2001
Fourier transform infrared emission spectroscopy of VCl
R. S. Ram
Department of Chemistry, University of Arizona, Tucson, Arizona 85721
P. F. Bernatha)
Department of Chemistry, University of Arizona, Tucson, Arizona 85721
and Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
S. P. Davis
Department of Physics, University of California, Berkeley, California 94720
͑Received 22 September 2000; accepted 21 December 2000͒
The high resolution spectrum of VCl has been observed in emission in the 3000–9400 cmϪ1 region
using a Fourier transform spectrometer. The bands were excited in a high temperature carbon tube
furnace from the reaction of vanadium metal vapor and a trace of BCl3 and the spectra were
recorded at a resolution of 0.05 cmϪ1. The new bands observed in the 6000–8000 cmϪ1 interval
have been attributed to VCl. The bands having R heads near 6176, 6589, 7004, 7358, and 7710 cmϪ1
5
have been assigned as the 0–2, 0–1, 0–0, 1–0, and 2–0 bands, respectively, of the 7.0 ⌬–X 5⌬
͓
͔
electronic transition. A rotational analysis of the ⌬1 –5⌬1 , ⌬2 –5⌬2 , and ⌬3 –5⌬3 subbands of
the 0–1 and 0–0 vibrational bands has been obtained and molecular constants have been extracted.
The remaining two of the five subbands could not be analyzed because of severe overlapping
from neighboring subbands. The principal molecular constants for the X 5⌬ state obtained
from the present analysis are: ⌬G(1/2)ϭ415.26(113) cmϪ1, Beϭ0.165 885(250) cmϪ1, ␣e
ϭ0.000 586(84) cmϪ1, and reϭ2.213 79(170) Å. Our work represents the first observation of this
near infrared electronic transition of VCl. © 2001 American Institute of Physics.
͓DOI: 10.1063/1.1349426͔
5
5
5
INTRODUCTION
electronic states have been predicted. For VF the ground
5
5
state was predicted to be either ⌬ or ⌸ but no definite
The study of transition metal-containing molecules has
attracted considerable recent attention because of their im-
portance in astrophysics1,2 and chemistry.3,4 These molecules
are also of theoretical interest.5–10 While most of the di-
atomic transition metal oxides11 and hydrides12 have been
relatively well characterized and many of the nitrides have
recently been investigated,13,14 only a few transition metal
halides have been studied so far. In the group 5 transition
metal family only limited low resolution data on VF,15
VCl,16 and TaCl17 are available in literature. Some visible
bands of VF have been observed by Jones and
Krishnamurty15 at low resolution and electronic assignments
conclusion was drawn about which state is lower in energy.20
19
5
On the other hand a ⌬ ground state was predicted for VH
on the basis of a high quality ab initio calculation.19 In gen-
eral, transition metal halides and hydrides have very similar
structure so we expect that the ground states of VF and VCl
5
are most probably ⌬ states.
In the present work we report on the observation of a
new electronic transition of VCl in the 6000–8000 cmϪ1
5
region. We have assigned this transition as 7.0 ⌬–X 5⌬. A
͓
͔
rotational analysis of the 0–0 and 0–1 bands of the
5
5
5⌬1 –5⌬1 , ⌬2 –5⌬2 , and ⌬3 –5⌬3 subbands has been ob-
tained. Although the rotational analysis of the remaining two
subbands (5⌬0Ϯ –5⌬0Ϯ , 5⌬4 –5⌬4) could not be obtained
because of overlapping from the other subbands, the present
assignment is consistent with the expectations based on the
ab initio calculations of Bruna for VH.19
5
5
of ⌺–5⌸ or ⌬–5⌸ have been proposed for these bands.
The emission spectrum of VCl has previously been observed
by Iacocca et al.16 in the visible region. This spectrum con-
sisted of only the ⌬ ϭ0 sequence bands and thus no vibra-
v
tional constants were obtained and no electronic assignments
were proposed. For TaCl, only a brief mention of a few
visible bands was made in a thesis17 where TaN bands were
produced from a microwave excitation of a TaCl4 vapor, N2,
and He mixture. Again no attempts were made to obtain the
vibrational or electronic assignments for the TaCl bands.
There is an ab initio calculation for the quintet states of
VF which proposes a ⌬ ground state. Some ab initio cal-
culations have been performed for VH by Bruna19 and VF by
Harrison20 and the spectroscopic properties for the low-lying
EXPERIMENT
The initial experiment was intended to observe VH
bands near 1 ␮m using the high temperature reaction of V
and H2. We have previously observed VH in a hollow cath-
ode discharge21 but the bands remain unanalyzed mainly be-
cause of strong perturbations. In the furnace we did not ob-
serve the VH bands and, therefore, decided to search for
bands of VF and VCl instead. The near infrared bands of
VCl were observed from the reaction of V atoms with BCl3
in a high temperature carbon tube furnace operated at a tem-
18
5
a͒
Electronic mail: bernath@uwaterloo.ca
0021-9606/2001/114(10)/4457/4/$18.00
4457
© 2001 American Institute of Physics
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 147.143.2.5
On: Sun, 21 Dec 2014 18:09:34

4458
J. Chem. Phys., Vol. 114, No. 10, 8 March 2001
Ram, Bernath, and Davis
ing hydrides. For example, the structure of TiF23 and TiCl24
closely resembles that of TiH25 and the electronic structure
of HfCl9 is similar to that of HfH.26 The VF and VCl mol-
19
5
ecules probably have a ⌬ ground state like VH and we
assign the observed VCl bands to a ⌬–5⌬ transition. The
5
0–0 band of this transition is located near 7004 cmϪ1, and
we have, therefore, decided to label this transition as
5
7.0 ⌬–X 5⌬.
͓
͔
5
The ⌬ states are expected to display Hund’s case ͑a͒
5
5
coupling leading to five subbands, ⌬0Ϯ –5⌬0Ϯ , ⌬1 –5⌬1 ,
5⌬2 –5⌬2 , ⌬3 –5⌬3 , and ⌬4 –5⌬4 . Normally ⌳ doubling
is expected to be small for ⌬ states and have J dependence27
given by J(Jϩ1) ⍀. However, mixing of the ground X 5⌬
5
5
FIG. 1. A compressed portion of the 7.0 5⌬–X 5⌬ transition of VC1.
͓
͔
͓
͔
5
perature of about 2200 °C. The emission from the furnace
was focused on to the entrance aperture of the 1 m Fourier
transform spectrometer of the National Solar Observatory at
Kitt Peak and the spectra were recorded using an InSb de-
tector and a RG 645 filter at a resolution of 0.05 cmϪ1. The
spectrum was recorded with only a single scan in about 3
min. In spite of this short integration time, the spectrum was
observed with sufficient signal-to-noise ratio for high resolu-
tion analysis.
A number of new bands observed in the 6000–8000
cmϪ1 region were readily attributed to VCl based on their
vibrational intervals and rotational line spacing. The spectral
line positions were measured using a data reduction program
called PC-DECOMP developed by Brault. The peak positions
were determined by fitting a Voigt line shape function to
each experimental feature. The observed spectra also con-
tained the vibration–rotation bands of HCl and HF as impu-
rities in addition to the VCl bands and V atomic lines. We
have used the HF22 line positions to calibrate our spectrum.
The molecular lines appear with a width of 0.070 cmϪ1 and
maximum signal-to noise ratio of about 8:1; the line wave
numbers are expected to be accurate to Ϯ0.007 cmϪ1. How-
ever, there is considerable overlapping and blending due to
the rotational structure of different subbands in the same re-
gion, so the uncertainty is somewhat higher for blended and
weaker lines.
state with the nearby ⌸ state ͓i.e., some Hund’s case ͑c͒
behavior͔ could lead to observable ⌳ doubling ͑or more cor-
rectly ⍀ doubling͒. The effects of ⌳ doubling should then be
apparent in the 5⌬1 –5⌬1 and 5⌬2 –5⌬2 subbands. In the
5⌬1 –5⌬1 subband the ⌳ doubling should increase as J (JH)
J, similar to that found in a normal ⌸–1⌸ transition. The
1
observed rotational structure of this subband is consistent
5
with this expectation. In the ⌬2 –5⌬2 subband the ⌳ dou-
2
bling, if present, should increase as J(Jϩ1) similar to a
͓
͔
3⌸2 –3⌸2 transition. The observed rotational structure of this
subband is also consistent with this expectation and a very
small doubling is seen at very high J values (JϾ63).
The observed pattern of ⌳ doubling in these two sub-
bands has been very helpful in the ⍀ assignment of different
subbands. Surprisingly some small ⍀ doubling has also been
5
observed in the ⌬3 –5⌬3 subband for JϾ82. This observa-
tion is consistent with some Hund’s case ͑c͒ behavior in the
lower state as discussed in the following. We have analyzed
5
the rotational structure of only the 5⌬1 –5⌬1 , ⌬2 –5⌬2 , and
5⌬3 –5⌬3 subbands in the 0–0 and 0–1 bands. The rotational
analysis of 0–2, 1–0, and 2–0 bands could not be achieved
because they were weak. The rotational structure of each
subband consists of R and P branches ͑no Q branch͒ appear-
ing with similar intensity indicating a ⌬⍀ϭ0 assignment.
The rotational constants for the different ⍀ states have been
obtained by fitting the observed lines to the following energy
level expression:
RESULTS AND DISCUSSION
2
Fv J͒ϭT ϩB J Jϩ1͒ϪD J Jϩ1͒
͓ ͑ ͔
͑
͑
v
v
v
A compressed portion of the observed spectrum is pre-
sented in Fig. 1. The bandheads observed near 6176, 6589,
7004, 7358, and 7710 cmϪ1 can readily be identified as the
0–2, 0–1, 0–0, 1–0, and 2–0 bands of a new electronic
transition. This transition has been assigned as a 5⌬–5⌬
transition. As seen in Fig. 1, the spectrum of each band is
very complex because of the crowded overlapping of the
rotational structure of different subbands. In fact, the over-
lapping is so severe that the rotational structure of all five
subbands could not be unambiguously identified. The recent
theoretical predictions for VH by Bruna19 were very helpful
in assigning our electronic transition. The ground state of
VH is predicted to be a 5⌬ state and a strong 5⌬–X 5⌬
transition has been predicted near 10 650 cmϪ1. Indeed, we
find a strong complex transition (5⌬–5⌬?) of VH20 near
7400 cmϪ1. In our previous studies of transition metal ha-
lides we have noted the similarity between the electronic
energy levels of transition metal halides and the correspond-
ϩHv J Jϩ1͒ 3Ϯ1/2 q J Jϩ1͒
͓ ͑
͔
͑
͕
v
3
ϩqD J Jϩ1͒ 2ϩqH J Jϩ1͒
͓ ͑ ͓ ͑
.
͔
͖
͑1͒
͔
v
v
The rotational lines were weighted according to resolu-
tion and the extent of blending. The badly blended lines were
heavily deweighted. The observed lines positions for the dif-
ferent subbands are available from EPAPS28 or from the au-
thors upon request. The molecular constants for the different
bands are provided in Table I. The e/f parity assignment in
the 5⌬1 –5⌬1 subband was made arbitrarily to provide a
positive ⌳-doubling constant qv in the X 5⌬1 spin compo-
5
5
nent. The parity assignments in the ⌬2 –5⌬2 and ⌬3 –5⌬3
subbands were also chosen arbitrarily. The higher order
⍀-doubling constant pD was also determined for the ϭ0
v
v
and 1 vibrational levels of the X 5⌬1 spin component. Like-
wise pD and pH were determined for the ϭ0 vibrational
v
v
v
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 147.143.2.5
On: Sun, 21 Dec 2014 18:09:34

J. Chem. Phys., Vol. 114, No. 10, 8 March 2001
Spectroscopy of VCl
4459
TABLE I. Spectroscopic constants for the 7.0 5⌬–X 5⌬ transition of VCl. a, b, c refer to the undetermined term values of the ϭ0 vibrational levels of
͓
͔
v
5
X
5⌬1 , X 5⌬2 , and X
⌬
spin components, respectively.
3
State
Tv
Bv
107ϫDv
1012ϫHv
103ϫqv
108ϫqD
1014ϫqH
v
v
v
5
7.0
7.0
7.0
⌬
⌬
⌬
0
0
0
cϩ6951.4112(14)
bϩ6985.9662(17)
aϩ7001.9264(21)
0.156 212 6͑63͒
0.154 722 8͑84͒
0.153 384͑11͒
1.7274͑41͒
1.2276͑78͒
1.049͑13͒
1.4043͑82͒
¯
¯
¯
¯
¯
¯
¯
¯
¯
͓
͓
͓
͔
͔
͔
3
2
1
5
5
¯
¯
1
0
1
0
1
0
cϩ413.6719(21)
0.165 385 6͑63͒
0.165 928 2͑62͒
0.165 098 6͑88͒
0.165 610 0͑86͒
0.164 532͑11͒
0.165 236͑18͒
1.1682͑40͒
1.1637͑37͒
0.9989͑99͒
0.9545͑87͒
1.211͑13͒
1.154͑13͒
¯
¯
¯
¯
¯
¯
6.18͑11͒
¯
5
X
X
X
⌬
⌬
⌬
c
¯
Ϫ0.566͑31͒
Ϫ1.568͑26͒
¯
¯
3
2
1
bϩ416.2044(25)
¯
5
5
b
¯
Ϫ0.1755͑34͒
Ϫ6.979͑25͒
Ϫ7.282͑30͒
¯
aϩ415.9116(29)
1.0642͑12͒
1.1133͑14͒
¯
a
¯
¯
5
5
5
level of the ⌬2 and ⌬3 spin components, respectively, of
the ground state. Note that no ⌳-doubling constants could be
determined for the excited state so they were set to zero.
Although the visible spectrum of VCl has been known
for decades, the identity of the ground state is still an open
question. The observation of several subbands in the near
infrared bands is consistent with the assignment of high mul-
tiplicity states. The previously suggested 5⌸ ground state
assignment for VF ͑or for VCl͒ is not consistent with the 5⌬
ground state of VH,19 although it may not be completely
ruled out. The observed bandhead positions have been used
to calculate the approximate vibrational constants for the
ground and excited states. Using the highest wave number
bandhead positions, the following approximate vibrational
constants have been determined for the ground and excited
ever, predict a ⌬ ground state as does a high level calcula-
tion on VH.19 Some valuable conclusions can be drawn from
the spectroscopic constants listed in Table I. As seen in
Table I, ⌳ doubling of significant magnitude has been ob-
tained in the X 5⌬1 spin component while no ⌳ doubling was
obtained in the 5⌬1 spin component of the excited state. This
5
indicates that the excited 7.0 ⌬ state is a relatively isolated
͓
͔
state whereas the X 5⌬1 spin component is mixed with a
nearby state. This is consistent with Harrison’s theoretical
predictions20 for VF. Averyanov and Khait18 predict that the
5⌸ state is 1700 cmϪ1 above the X 5⌬ state for VF, while the
corresponding value for VH is about 800 cmϪ1
.
As for other transition metal halides, useful information
about electronic structure can be derived from the atomic
energy levels29 of Vϩ. The lowest term of Vϩ is a 5D de-
rived from the 3d4 configuration. The ligand field of ClϪ
states: ␻eЉϭ417 cmϪ1, ␻exeЉϭ1 cmϪ1, ␻Јϭ356 cmϪ1, and
e
will split this term into ⌬, ⌸, ⌺Ϫ states in order of in-
creasing energy. This prediction is borne out by the calcula-
tions on VF18,20 and VH.19 The next term in Vϩ is a 5F at
about 3000 cmϪ1 arising from the 3d34s1 configuration.
5
5
5
␻exeЈϭ1 cmϪ1. The rotational constants obtained for the
v
ϭ0 and 1 vibrational levels can be used to determine the
5
5
5
equilibrium rotational constants for the ⌬1 , ⌬2 , and ⌬3
spin components of the ground state. The values of Be
This term correlates to the 5⌽, ⌬, ⌸, ⌺ϩ cluster of states
found in the 7000–10 000 cmϪ1 range for VH. Our 5⌬–X 5⌬
transition is thus between the two 5⌬ states derived from the
lowest energy a 5D and a 5F terms of Vϩ.
5
5
5
ϭ0.165 588(21) cmϪ1
,
␣eϭ0.000 704(21) cmϪ1 for the
X 5⌬1 , Beϭ0.165 866(11) cmϪ1, ␣eϭ0.000 511(12) cmϪ1
for the X 5⌬2 and Beϭ0.166 199 5(76) cmϪ1
,
␣
e
ϭ0.000 542 6(88) cmϪ1 for the X 5⌬3 spin component have
been obtained. The observed term values for the three spin
components provide the ⌬G(1/2) vibrational intervals of
415.9116͑29͒ cmϪ1, 416.2044͑25͒ cmϪ1, and 413.6719͑21͒
cmϪ1 for the X 5⌬1 , X 5⌬2 , and X 5⌬3 spin components,
respectively. The irregular variation in the vibrational inter-
vals can be attributed to the interactions with the slightly
CONCLUSION
We have observed the thermal emission spectrum of VCl
in the 3000–9400 cmϪ1 region using a Fourier transform
spectrometer. Five groups of bands with R heads ͑for the
highest wave number subbands͒ near 6176, 6589, 7004,
7358, and 7710 cmϪ1 have been assigned as the 0–2, 0–1,
5
higher-lying ⌸ state. The three subbands analyzed in this
work involve the three middle spin components of the
ground and excited states, the average of the effective
⌬G(1/2), Be and ␣e values need to be computed to derive
the Hund’s case ͑a͒ constants for the ground and excited
0–0, 1–0, and 2–0 bands of the 7.0 ⌬–X 5⌬ transition. A
5
͓
͔
rotational analysis of the 5⌬1 –5⌬1 , 5⌬2 –5⌬2 , and
5⌬3 –5⌬3 subbands of the 0–1 and 0–0 bands has been ob-
tained and molecular constants have been extracted. Most
likely the lower X 5⌬ state is the ground state but we do not
have any direct evidence to prove this. Further experimental
and theoretical work on VCl will be necessary to test our
proposed assignment, and this work is under way.
states.
This
calculation
provides
⌬G(1/2)
ϭ415.26(113) cmϪ1
,
Beϭ0.165 885(250) cmϪ1
,
␣
e
ϭ0.000 856(84) cmϪ1 for the ground X 5⌬ state. The equi-
librium rotational constant results in the equilibrium ground
state bond length of reЉϭ2.213 79(170) Å. A value of r0Ј
ϭ2.291 88(110) Å has been obtained for the excited state
ACKNOWLEDGMENTS
using the average value of B0Јϭ0.154 773(150) cmϪ1
.
The previous ab initio calculation of Harrison20 on VF
did not lead to a definite conclusion about the identity of the
ground state ͑either 5⌬ or 5⌸͒. Averyanov and Khait,18 how-
We thank J. Wagner, C. Plymate, and M. Dulick of the
National Solar Observatory for assistance in obtaining the
spectra. The National Solar Observatory is operated by the
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 147.143.2.5
On: Sun, 21 Dec 2014 18:09:34

4460
J. Chem. Phys., Vol. 114, No. 10, 8 March 2001
Ram, Bernath, and Davis
Association of Universities for Research in Astronomy, Inc.,
under contract with the National Science Foundation. The
research described here was supported by funding from
NASA laboratory astrophysics program. Some support was
also provided by the Natural Sciences and Engineering Re-
search Council of Canada.
13 W. J. Balfour, C. X. W. Qian, and C. Zhou, J. Chem. Phys. 106, 4383
͑1997͒, and references therein.
14 R. S. Ram and P. F. Bernath, J. Mol. Spectrosc. 184, 401 ͑1997͒, and
references therein.
15 W. E. Jones and G. Krishnamurty, J. Phys. B 13, 3375 ͑1980͒.
16 D. Iacocca, A. Chatalic, P. Deschamps, and G. Pannetier, C. R. Acad. Sci.,
Paris C271, 669 ͑1970͒.
17 T. M. Dunn ͑private communication͒.
1 C. Jascheck and M. Jascheck, The Behavior of Chemical Elements in Stars
͑Cambridge University Press, Cambridge, 1995͒.
18 A. S. Averyanov and Y. G. Khait, Opt. Spectrosc. 67, 829 ͑1990͒.
19 P. J. Bruna ͑private communication͒; J. Anglada, P. J. Bruna, and S.
Peyerimhoff ͑unpublished͒.
2 J. D. Kirkpatrick, I. N. Reid, J. Liebert, R. M. Cutri, B. Nelson, C. Be-
ichman, C. C. Dahn, D. G. Monet, J. E. Gizis, and M. F. Skrutskie,
Astrophys. J. 519, 802 ͑1999͒.
20 J. F. Harrison ͑private communication͒.
21 R. S. Ram and P. F. Bernath ͑unpublished͒.
22 R. B. LeBlanc, J. B. White, and P. F. Bernath, J. Mol. Spectrosc. 164, 574
͑1994͒.
3 M. Grunze, in The Chemical Physics of Solid Surfaces and Heterogeneous
Catalysis, edited by D. A. King and D. P. Woodruff ͑Elsevier, New York,
1982͒, Vol. 4, p. 143.
23 R. S. Ram, J. R. D. Peers, Y. Teng, A. G. Adam, A. Muntianu, P. F.
Bernath, and S. P. Davis, J. Mol. Spectrosc. 184, 186 ͑1997͒.
24 R. S. Ram and P. F. Bernath, J. Mol. Spectrosc. 186, 113 ͑1997͒.
25 J. Anglada, P. J. Bruna, and S. D. Peyerimhoff, Mol. Phys. 69, 281 ͑1990͒.
26 R. S. Ram and P. F. Bernath, J. Chem. Phys. 101, 74 ͑1994͒.
27 J. M. Brown, A. S.-C. Cheung, and A. J. Merer, J. Mol. Spectrosc. 124,
464 ͑1987͒.
28 See EPAPS Document No. EJCPSA6-114-015111 for line positions for
the near infared transition of VCl. This document may be retrieved via the
EPAPS homepage ͑http://www.AIP.org/pubservs/epaps.html͒ or from ft-
p.AIP.org in the directory/epaps/. See the EPAPS homepage for more in-
formation.
29 C. E. Moore, Atomic Energy Levels ͑USGPO, Washington, DC, 1971͒,
Vol. 1, NSRDS-NBS 35.
4 F. A. Cotton, G. Wilkinson, C. A. Murillo, and M. Bochmann, Advanced
Inorganic Chemistry ͑Wiley, New York, 1999͒, 6th ed.
5 G. Freindorf, C. M. Marian, and B. A. Hess, J. Chem. Phys. 99, 1215
͑1993͒.
6 S. R. Langhoff and C. W. Bauschlicher, Jr., J. Mol. Spectrosc. 141, 243
͑1990͒.
7 C. W. Bauschlicher, Jr., Theor. Chem. Acc. 103, 141 ͑2000͒.
8
´
R. S. Ram, J. Lievin, and P. F. Bernath, J. Chem. Phys. 109, 6329 ͑1998͒.
9
´
R. S. Ram, A. G. Adam, A. Tsouli, J. Lievin, and P. F. Bernath, J. Mol.
Spectrosc. 202, 116 ͑2000͒.
10
´
R. S. Ram, A. Tsouli, J. Lievin, A. G. Adam, W. Sha, and P. F. Bernath,
J. Chem. Phys. ͑in press͒.
11 A. J. Merer, Annu. Rev. Phys. Chem. 40, 407 ͑1989͒.
12 P. F. Bernath, in Advances in Metal and Semiconductor Clusters, edited
by M. Duncan ͑Elsevier, New York, 2001͒.
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 147.143.2.5
On: Sun, 21 Dec 2014 18:09:34