Cavity ring-down laser absorption spectroscopy of the E3Δ- X3Δ transition of VN

Article abstract of DOI:10.1021/jp049441l

The (0,0) band of the electronic transition of VN near 450.5 nm has been investigated using the technique of laser vaporization/reaction with free jet expansion and cavity ring-down laser absorption spectroscopy. A new transition system was observed, which has been assigned as the E³Δ-X ³Δ system. All three ΔΩ = 0 subband transitions were recorded and rotationally analyzed. A least-squares fit of the measured line positions yielded molecular constants for the new E³Δ state. The bond length, r_o, of the E³Δ state was determined to be 1.6937 A, which is the longest among the known states of VN. The E³Δ state is expected to arise from the electronic configuration 1δ¹10σ¹, where the 10σ orbital is an antibonding orbital. A comparison of the observed electronic states of VN to those of the isoelectronic TiO molecule supports the assignment.

Full text of DOI:10.1021/jp049441l

J. Phys. Chem. A 2004, 108, 5333-5337
5333
Cavity Ring-Down Laser Absorption Spectroscopy of the E3∆-X3∆ Transition of VN
Tongmei Ma, J. W-H. Leung, and A. S-C. Cheung*
Department of Chemistry, The UniVersity of Hong Kong, Pokfulam Road, Hong Kong
ReceiVed: February 6, 2004; In Final Form: March 15, 2004
The (0,0) band of the electronic transition of VN near 450.5 nm has been investigated using the technique of
laser vaporization/reaction with free jet expansion and cavity ring-down laser absorption spectroscopy. A
new transition system was observed, which has been assigned as the E3∆-X3∆ system. All three ∆Ω ) 0
subband transitions were recorded and rotationally analyzed. A least-squares fit of the measured line positions
yielded molecular constants for the new E3∆ state. The bond length, ro, of the E3∆ state was determined to
be 1.6937 Å, which is the longest among the known states of VN. The E3∆ state is expected to arise from
the electronic configuration 1δ110σ1, where the 10σ orbital is an antibonding orbital. A comparison of the
observed electronic states of VN to those of the isoelectronic TiO molecule supports the assignment.
Introduction
retrieve rotational and spin fine constants for the new E3∆ state.
In addition, with the use of a molecular orbital energy level
Interest in the electronic structure of diatomic molecules
containing transition metals has increased in the past decades.1-6
The importance of these transition metal diatomics ranges from
catalysis7,8 and surface science9 to astrophysics.5,6,10 Spectro-
scopic studies of these diatomic molecules provide important
data needed for the understanding of various catalytic processes
and chemical bonding in simple metal-containing systems.3
Transition metal nitrides, in particular, are important in inorganic
and biological systems in the industrial fixation of nitrogen.11
It is well known that transition metal oxide and hydride spectra
are observed in the atmosphere of cool M- and S-type
stars.10,12,13 Because of high cosmic abundances of transition
elements in stellar objects, it is possible that transition metal
nitride molecules may also be found there.
Within the first transition metal period, there has been
considerable interest in the spectroscopic properties of vanadium-
containing molecules, which include vanadium oxide,14-19
halides,20,21 sulfide,22 and nitride.23-30 This paper deals with the
spectroscopic study of VN. The electronic transitions of VN
were first studied by Peter and Dunn23 and Simard et al.24 using
conventional grating and laser-induced fluorescence spectro-
scopy (LIFS), respectively. Peter and Dunn23 recorded the
A3Φ-X3∆ transition and performed rotational analysis of the
(0,0) band. Simard et al.24 reported rotational analysis of the
intercombination d1Σ+-X3∆1 system. Balfour et al.,25 using a
molecular beam source and LIFS, studied the rotational and
hyperfine structure of the D3Π-X3∆ (0,0) transition and
reported accurate rotational and hyperfine constants for both
the D3Π and the X3∆ states. The permanent electric dipole
moments of the D3Π and X3∆ states were measured experi-
mentally by Steimle et al.28 The spectroscopic properties of the
low-lying singlet states have recently been studied both theoreti-
cally26 and experimentally.29,30
diagram, the spectroscopic properties of electronic states arising
from various electronic configurations of both the VN and the
isoelectronic TiO molecules are compared.
Experiment Details
The laser vaporization/reaction free jet expansion apparatus
and the cavity ring-down laser absorption experimental setup
employed in this work have been described previously.32 Only
a brief description of the experimental conditions is given here.
VN molecules were produced by the reaction of laser-vaporized
vanadium atoms with ammonia (NH3). Pulses of 532 nm, 9-10
mJ, and 10 ns from a Nd:YAG laser were focused onto the
surface of a vanadium metal rod to generate vanadium atoms.
A pulsed valve with appropriate delay released a mixture of
2% NH3 in helium gas to react with the laser-ablated vanadium
atoms. We were also able to produce VN using 0.03% phenyl
hydrazine (C6H5NHNH2) in helium; however, the signal ob-
tained was generally weaker than those obtained using NH3.
Phenyl hydrazine is a potential nitrogen precursor for use in
metal oxide chemical vapor deposition (MOCVD) processes.
The operating cycle of the Nd:YAG laser-pulsed valve system
was 10 Hz. The backing pressure at the pulsed valve was set to
5 atm. The tunable laser pulses in the visible region were
produced by a dye laser pumped by a Nd:YAG laser system.
Two sets of high-reflectance mirrors and two different dyes
(Coumarin 460 and Coumarin 503) were necessary to cover
the spectral region between 440 and 520 nm. The laser
wavelength was calibrated using signals from an optogalvanic
cell filled with argon and xenon gases. The dye laser line width
was about 0.06 cm-1, and typical pulse energy used in the
experiments was 1-3 mJ. The cavity ring-down absorption
signal was detected by a photomultiplier tube and fed to a
preamplifier before being forwarded to a digital oscilloscope
and eventually transferred to a computer for storage. All events
for recording the CRLAS signal were coordinated and synchro-
nized by a digital delay generator. It was found that shot-to-
shot fluctuation of the cavity ring-down absorption signal was
severe, and a steady rotation of the metal rod is necessary to
avoid ablating a particular surface for more than a few minutes.
Typically, 8-10 laser shots were averaged per data point to
maintain an adequate signal-to-noise ratio spectrum. The
maximum empty-cavity decay time (1/e) for the ring-down
In this paper, we report rotationally resolved spectra of a new
electronic transition, namely the E3∆-X3∆ system of VN, using
the technique of laser vaporization/reaction with supersonic
cooling and cavity ring-down laser absorption spectroscopy
(CRLAS).31 The (0,0) band of the E3∆-X3∆ transition was
recorded and analyzed. Measured line positions were fit to
* To whom correspondence should be addressed. Fax: (852) 2857-1586.
Tel.: (852) 2859-2155. E-mail: hrsccsc@hku.hk.
10.1021/jp049441l CCC: $27.50 © 2004 American Chemical Society
Published on Web 05/26/2004

5334 J. Phys. Chem. A, Vol. 108, No. 25, 2004
Ma et al.
TABLE 1: Assigned Rotational Transition Lines of the E3∆-X3∆ (0,0) Band of VN (cm-1
)
J
P1
Q1
R1
P2
Q2
R2
P3
Q3
R3
1
22 194.84
94.44
22 196.91
97.60
98.10
98.54a
98.54a
98.54a
98.34
97.90
97.31
96.53
95.56
94.43
93.07
2
22 192.26
90.67
88.81
86.81
84.71
82.44
79.92
77.22
74.36
71.27
67.93
64.51
22 186.81
86.22
22 190.14a
90.67a
91.03a
91.19a
91.19a
91.03a
90.67a
90.14a
89.42
3
93.90
22 183.13
81.35
79.38
77.22
74.96
72.46
69.72
66.81
63.89
60.70
57.26
53.70
49.89
45.98
41.93
37.63
22 182.70
82.98
83.26a
83.26a
83.13
82.70
82.19
81.47
80.60
79.38
78.27
76.75
75.20
4
93.07
85.53
22 177.63
76.73
5
92.33
84.71
22 171.36
69.10
66.81
64.28
61.62
58.72
55.65
52.41
48.92
45.32
41.59
37.63
33.55
29.19
6
91.19
83.67
75.66
7
82.44
74.39
8
81.05
72.96
9
71.34
10
11
12
13
14
15
16
17
18
88.53
87.48
86.22
84.82
83.26
81.47
79.61
a Blended line.
transition, is barely noticeable at 22 183 cm-1. Unlike some
transition metal diatomic molecules that have been studied, iso-
topic shifts can be used to confirm the vibrational quantum
number of the upper state. VN has no naturally occurring isotope
with appreciable abundance. We performed the same experiment
again using 2% 15NH3 in helium and recorded a portion of the
V15N spectrum near the band head region at 22 198 cm-1. A
comparison of the R head of the V14N and V15N spectra shows
an isotopic shift of less than 0.1 cm-1, which indicates clearly
that the transition belongs to the ∆V ) 0 sequence. Furthermore,
the laser vaporization/reaction free jet expansion source is a low-
temperature molecular source, which normally populates the V
) 0 level of the ground state. Rotational analysis indicated that
the lower state B value agrees well with the known B0 value of
the X3∆ state. Therefore, the observed band is assigned as the
(0,0) band of E3∆-X3∆ transition. We searched the wavelength
region longer than 450.5 nm and no other VN band was ob-
served, which is consistent with the assignment of the (0,0) band.
Strong R1 and P1 branches are readily identified near the band
head region. The line assignment was relatively simple because
ground-state combination differences, ∆2F′′, can be calculated
from published constants.23 For a 3∆ (case a)-3∆ (case a) tran-
sition, the main branches are P1, Q1, R1; P2, Q2, R2; and P3, Q3,
R3. We observed all of these main branches. A list of the mea-
sured line positions is given in Table 1. Because of relatively
large spin-orbit separations, the population of the higher spin-
orbit components, X3∆2 and X3∆3, are low and the transition
intensity is generally weak for these subband transitions. For
the stronger E3∆1-X3∆1 subband, the lowest observed J num-
bers for P1, Q1, and R1 branches are 2, 1, and 1, respectively,
which allows the establishment of the component Ω′′ ) Ω′ )
1 for both states. Close examination of the Q1(1) and R1(1) lines
shows that the line widths of these two lines are wider than the
expected Doppler line width. This is because the X3∆ state arises
from the electronic configuration involves an unpaired electron
in the sσ orbital formed mainly from the vanadium atom 4s
orbital, resulting in a large Fermi contact interaction and a large
hyperfine splitting.25 The coupling scheme for the X3∆ state
conforms to the Hund’s case aâ, and the hyperfine width
collapses quickly as J increases.
Figure 1. Cavity ring-down laser absorption spectrum of the (0,0)
band of the E3∆-X3∆ transition of VN.
signal was about 40 µs at 460 nm, corresponding to a loss per
pass of about 60 ppm. For the VN spectrum, the highest signal
obtained was about 440 ppm. Regular cleaning of the mirrors
was necessary to avoid interference arising from the deposition
of laser-ablated material. The measured VN lines obtained were
calibrated with direct readings from the grating values of the
dye laser and converted to vacuum wavelength33 and then to
wavenumbers. The estimated absolute accuracy is about (0.2
cm-1; however, the relative accuracy should be better than (0.1
cm-1. To obtain information about the vibrational level of the
upper state, we also repeated the experiment using 15NH3.
Results and Discussion
General Features. The cavity ring-down laser absorption
spectrum of VN in the visible region between 440 and 520 nm
has been observed and analyzed. The observed band near 450.5
nm shows strong P and R branches, which indicate that the
transition is consistent with ∆Λ ) 0. Detailed rotational analysis
confirms that the transition is a 3∆-3∆ system. By comparison
with TiO, a molecule that is isoelectronic with VN, the upper
state is probably the fifth triplet excited state, so it is labeled as
the E3∆-X3∆ transition.
Determination of Spectroscopic Parameters. The effective
3
molecular Hamiltonian for a ∆ state is given34 by
Figure 1 shows the band head region with a resolution of
about 0.06 cm-1. It is clearly seen that two subband heads occur
at 22 198 and 22 191 cm-1, which correspond to the E3∆1-
X3∆1 and E3∆2-X3∆2 subband transitions, respectively. The
head of the third subband, corresponding to the E3∆3-X3∆3
2
3
Hˆ eff ) BRˆ2 - DRˆ4 + ALˆz Sˆz + λ(3Sˆz2 - Sˆ2) +
1
2
1
3
AD[Lˆz Sˆz, Rˆ2]+ + λD[3Sˆz2 - Sˆ2,Rˆ2]+ (1)

Cavity Ring-Down Laser Absorption Spectroscopy of VN
J. Phys. Chem. A, Vol. 108, No. 25, 2004 5335
TABLE 2: Molecular Constants for the X3∆ and E3∆ States
TABLE 3: Spectroscopic Constants for Low-Lying Triplet
of VN (cm-1
)
and Singlet States of TiO and VN (cm-1
)
parameter
X3∆a
E3∆
elect config
state
TiO
state
VN
To
0
22 187.339(9)
0.534 999(74)
0.3 ×10-6 b
9σ11δ1
X3∆
Be ) 0.534 51
re ) 1.6202a
A ) 50.65
X3∆
Bo ) 0.625 328
ro ) 1.5666a
A ) 75.503
B
0.625 328
D
A
AD
λ
λD
rms
BΩ)1,eff
BΩ)2,eff
BΩ)3,eff
0.91 × 10-6
75.503 96
71.44(6)
9σ14π1
E3Π
To ) 11 925.03
Bo ) 0.5155
rσ ) 1.6512
A ) 86.86
-0.025 46
3.369 88
0.95(5) × 10-4
3.08(9)
-0.0129 × 10-3
-0.0010(7) × 10-3
0.05
1δ2
1δ14π1
D3Σ- To ) 12 284
0.528 24(17)
0.536 40(27)
0.541 72(39)
A3Φ
B3Π
C3∆
To ) 14 094.173 A3Φ
To ) 14 313.247
Bo ) 0.610 85
ro ) 1.5851
A ) 78
Bo ) 0.505 69
ro ) 1.6671
a Values taken from ref 25. b Value fixed in least-squares fit.
A ) 57.3668
1δ14π1
To ) 16 147
Bo ) 0.506 174
ro ) 1.6663
A ) 20.81
D3Π
E3∆
a1∆
To ) 16 026.191
Bo ) 0.609 145
ro ) 1.5872
A ) 54.567
1δ110σ1
To ) 19 339.73
Bo ) 0.489 88
ro ) 1.6938
A ) 46.1
To ) 22 187.339
Bo ) 0.534 99
ro ) 1.6937
A ) 71.43
9σ11δ1
9σ2
a1∆
To ) 3444.367
Bo ) 0.536 287
ro(Å) ) 1.6189
To ) a
Bo ) 0.634 792
ro(Å) ) 1.5549
d1Σ+
b1Π
To ) 5663
Bo ) 0.547 702
ro ) 1.6019
b1Σ+ To ) 10 952.69
Bo ) 0.617 896
ro ) 1.5760
9σ14π1
1δ2
To ) 14 717.185
Bo ) 0.511 99
ro ) 1.6568
d1Σ+ To ) 16 220.187
Be ) 0.62 861
re ) 1.5625
1δ14π1
1δ14π1
1δ110σ1
9σ110σ1
e1Π
To ) a + 14 292.76
Bo ) 0.619 123
ro ) 1.5744
Figure 2. Molecular orbital energy level diagram of VN.
c1Φ
f1∆
To ) 21 284.957 f1Φ
Bo ) 0.521 366
To ) a + 17 432.31
Bo ) 0.616 718
ro ) 1.57754
where [x,y]+ ) xy + yx is the anticommutator necessary to
preserve the Hermitian form of the Hamiltonian matrix. B and
D are respectively the rotational constant and its centrifugal
distortion; A and λ are respectively the first-order and second-
order spin-orbit parameters; their centrifugal distortion cor-
rections are respectively AD and λD. Matrix elements for the
Hamiltonian matrix can be found in papers by Brown et al.35
and Balfour et al.25 Least-squares fitting of the observed line
positions were performed in two stages. First, the P, Q, and R
branches of each subband were fit individually to obtain the
effective rotational constant, BΩ,eff, and the subband origin.
Subsequently, all the transition line positions were merged
ro ) 1.6419
To ) 22 513.355
Bo ) 0.502 363
ro ) 1.6726
e1Σ+
To ) 29 960.592
Bo ) 0.488 25
ro ) 1.6966
a re and r are in Å unit.
°
The observed electronic states can easily be understood from
this molecular orbital diagram. We compare the spectroscopic
properties of electronic states of VN with those of the isoelec-
tronic TiO molecule to better understand the newly observed
E3∆ state. The electronic configurations giving rise to the
observed ground and low-lying electronic states are
3
together and fit to a Hamiltonian matrix for the ∆ state for
both excited and ground states. Since Balfour et al.25 obtained
accurate molecular constants for the V ) 0 level of the X3∆
state, their values were used and held fixed in the fit. The root-
mean-square error of the final fit was 0.05 cm-1. Molecular
constants obtained are listed in Table 2. The experimentally
determined bond length, ro, for the E3∆ state is 1.6937 Å.
8σ23π49σ11δ1
8σ23π49σ2
X3∆, a1∆
1Σ
(2)
(3)
(4)
(5)
(6)
(7)
(8)
8σ23π49σ14π1
8σ23π41δ2
3Π, 1Π
1Σ+, 3Σ-, 1Γ
1Π, 3Π, 1Φ, 3Φ
3∆, 1∆
8σ23π41δ14π1
8σ23π41δ110σ1
8σ23π49σ110σ1
Electronic Configurations. Ab initio calculations performed
by Harrison26 indicate that the energy order of excited electronic
states of VN is very similar to that of the isoelectronic TiO
molecule.36-38 Figure 2 shows a molecular orbital (MO) energy
level diagram of VN formed from the vanadium 4s and 3d
atomic orbitals (AOs) and the nitrogen 2p AOs. The lower
energy 8σ and 3π MOs and the higher energy antibonding 10σ
and 4π MOs are formed from the nitrogen 2p AO and vanadium
3dσ, 3dπ, 4pσ, and 4pπ AOs. The 9σ MO is essentially a
vanadium 4s AO. The 1δ MO is almost a pure vanadium 3dδ
AO because there is no other orbital of δ symmetry lying nearby.
3Σ+, 1Σ+
These single electronic configuration explanations are sim-
plistic; however, they lead to a good understanding of the ground
and many low-lying electronic states. Table 3 lists the spectro-
scopic parameters for the low-lying singlet and triplet states
observed for TiO and VN. The electronic states arising from
the same electronic configuration in TiO and VN are put side
by side and are arranged in the order of increasing energy. For
simplicity, the triplet states and singlet states are listed

5336 J. Phys. Chem. A, Vol. 108, No. 25, 2004
Ma et al.
separately. For historical reasons, the letter designations of these
states (A, B, C, ..., a, b, c, ...) do not follow their energetic
ordering. This situation shows clearly that experimentalists
sometimes have difficulties in assigning correct labels to the
state found when only partial knowledge of the electronic
structure of a molecule is available. The six triplet states
expected from the electronic configurations (2), (4)-(8) are all
found in TiO. Except for the D3Σ- state, all of the triplet states
are well characterized. For VN, only four triplets state are
known; since the newly observed 3∆ state found in this work is
higher in energy than the D3Π state, it is labeled accordingly
as the E3∆ state. The observed E3∆-X3∆ transition is expected
to come from the promotion of an electron from the 9σ MO to
the 10σ MO. From the MO energy level diagram in Figure 2,
it is apparent that the 10σ MO is antibonding in nature. When
an electron is removed from a bonding orbital and placed into
an antibonding orbital, the bond length of the molecule increases.
Increases in bond length by 0.0736 and 0.1271 Å from the
LIFS;31 however, CRLAS has the advantage of not being related
to the relaxation pathways of molecules in the excited state.
Even though this advantage is not particularly important for
many diatomic or small molecules, for medium- to large-size
polyatomic molecules such an advantage is significant because
the quantum yield for fluorescence is generally very low. The
CRLAS instrument used for the present study is very similar
to the one used by Saykally and co-workers31 for studying the
spectroscopic properties of gas-phase metal-containing transient
species. In our experimental setup, various transient diatomic
and polyatomic species can be produced using the laser
vaporization/reaction source31,40,41 that allows vaporized atoms
or chemical compounds to react with other reagent chemicals
seeded in a carrier gas. The combination of such a laser
vaporization/reaction source and CRLAS is a powerful tool for
studying the spectroscopy of medium- to large-size transient
molecules. We plan to pursue further spectroscopic work on
transient polyatmoic species using this instrumental setup.
3
ground to the excited ∆ state are found respectively for TiO
and VN, confirming this expectation. In fact, the C3∆ state of
TiO and the E3∆ state of VN have the longest bond lengths.
Another piece of evidence confirming that the observed E3∆
state belongs to the electronic configuration of 1δ110σ1 can be
found by comparing the spin-orbit separation of the three spin-
orbit components. The separation of the highest and lowest
spin-orbit components in a degenerate multiplet state is equal
to 2AΛS when other high-order spin-orbit effects are ignored.
For the X3∆ and E3∆ states of VN, the separations are
respectively 302 and 286 cm-1. These values can be correlated
to the atomic spin-orbit parameter by applying the microscopic
spin-orbit Hamiltonian,39 Hˆ so ) ∑i aili‚si. This is a single-
electron operator that can be applied to the Slater determinant
wave function. Taking the electronic configuration as 9σ11δ1
X3∆ and 1δ110σ1 E3∆, the wave function for the Ω ) 3
component is
Acknowledgment. The work described here was supported
by a grant from the Research Grants Council of the Hong Kong
Special Administrative Region, China (Project No. HKU 7138/
99P). We thank Dr. S. J. Xu for his continuous support in this
research and the reviewer for suggestions to improve the text.
References and Notes
(1) Huber, K. P.; Herzberg, G. Constants of Diatomic Molecules; van
Nostrand: New York, 1979.
(2) Bauschlicher, C. W., Jr.; Walch, S. P.; Langhoff, S. R. In Quantum
Chemistry: The Challenge of Transition Metals and Chemistry; Veillard,
A., Ed.; NATO ASI Series C; Reidel: Dordrecht, 1986.
(3) Langhoff, S. R.; Bauschlicher, C. W., Jr. Annu. ReV. Phys. Chem.
1988, 39, 181.
(4) Merer, A. J. Annu. ReV. Phys. Chem. 1989, 40, 407.
(5) Hirota, E. Rep. Prog. Chem., Sect. C: Phys. Chem. 2000, 96, 95.
(6) Bernath, P. F. Rep. Prog. Chem., Sect. C: Phys. Chem. 2000, 96,
177.
(7) Grunze, M. In The Chemical Physics of Solid Surfaces and
Heterogeneous Catalysis; King, D. A., Woodruf, D. P., Eds.; Elsevier: New
York, 1982; Vol. 4, p 143.
(8) Rao, C. N. R. Annu. ReV. Phys. Chem. 1989, 40, 291.
(9) Wojuechowsba, M.; Habu, J.; Lomnicki, S.; Stoch, J. J. Mol. Catal.
A: Chem. 1999, 141, 155.
3
| ∆3, σ1δ1 ) | σRδ+R|
Thus,
(10) Joyce, R. R.; Hinkle, K. H.; Wallace, L.; Dulick, M.; Lambert, D.
L. Astrophys. J. 1998, 116, 2520.
(11) Nishibayashi, Y.; Iwai, S. Hidai, M. Science 1998, 279, 540.
(12) Lambert, D. L.; Clegg, R. E. S. Mol. Not. R., Astron. Soc. 1980,
191, 367.
3
3∆3, σ1δ1 | Hˆ so | ∆3,σ1δ1
)
σRδ+R |
a l ‚ s | σRδ+R ) R
∑
i
i zi
zi
δ
(13) Lindgren, B.; Olofsson, G. Astron. Astro. Phys. 1980, 84, 303.
(14) Cheung, A. S-C.; Hansen, R. C.; Merer, A. J. J. Mol. Spectrosc.
1982, 91, 165.
(15) Cheung, A. S-C.; Taylor, A. W.; Merer, A. J. J. Mol. Spectrosc.
1982, 92, 391.
(16) Merer, A. J.; Huang, G.; Cheung, A. S-C.; Taylor, A. W. J. Mol.
Spectrosc. 1987, 125, 465.
(17) Cheung, A. S-C.; Hajigeorgiou, P. G.; Huang, G.; Huang, S.-Z.;
Merer, A. J. J. Mol. Spectrosc. 1994, 163, 443.
(18) Adam, A. G.; Barues, M.; Berno, B.; Bower, R. D.; Merer, A. J. J.
Mol. Spectrosc. 1995, 170, 94.
(19) Ram, R. S.; Bernath, P. F.; Davis, S. P.; Merer, A. J. J. Mol.
Spectrosc. 2002, 211, 279.
(20) Ram, R. S.; Bernath, P. F.; Davis, S. P. J. Chem. Phys. 2001, 114,
4457.
(21) Ram, R. S.; Bernath, P. F.; Davis, S. P. J. Chem. Phys. 2002, 116,
3
Similarly, for the Ω ) 1 component, the 3∆1,σ1δ1 | Hˆ so | ∆1,
σ1δ1 ) -aδ. Therefore, the spin-orbit separation for a ∆
3
state in a σ1δ1 electronic configuration is equal to 2aδ. Since
the δ MO must be essentially unchanged from its shape in the
atom or ion, the aδ parameter is equivalent to the atomic ς3d
value (151 cm-1).39 It is easily seen that there is good agreement
between the spin-orbit separations of 302 and 286 cm-1 for
the two 3∆ states of VN and that of 2aδ (302 cm-1) for the V+
ion, which confirms that the electronic configuration of the X3∆
and E3∆ states does indeed arise from the σ1δ1 configuration.
A review of the literature indicates that many transient
diatomic and small-metal-containing compounds1,4-6 have been
studied using laser-induced fluorescence spectroscopy (LIFS),
which is a sensitive technique. The detection of LIF signal relies
on the excited molecule dissipating its excess energy through
fluorescence. CRLAS is also a sensitive technique, which is
suitable for studying transient molecules produced with very
low number density or transitions with weak intensity. Saykally
and co-workers31 have demonstrated the application of this
technique and have discussed the associated theory in detail.
The sensitivity of CRLAS is somewhat comparable to that of
7035.
(22) Ran, Q.; Tam, W. S.; Cheung, A. S-C.; Merer, A. J. J. Mol.
Spectrosc. 2003, 220, 87.
(23) Peter, S. L.; Dunn, T. M. J. Chem. Phys. 1989, 90, 5333.
(24) Simard, B.; Clasoni, C.; Hackett, P. A. J. Mol. Spectrosc. 1989,
136, 44.
(25) Balfour, W. J.; Merer, A. J.; Nicki, H.; Simard, B.; Hackett, P. A.
J. Chem. Phys. 1993, 99, 3288.
(26) Harrison, J. F. J. Phys. Chem. 1996, 100, 3513.
(27) Andrews, L.; Bare, W. D.; Chertihin, G. V. J. Phys. Chem. 1997,
101, 8417.

Cavity Ring-Down Laser Absorption Spectroscopy of VN
J. Phys. Chem. A, Vol. 108, No. 25, 2004 5337
(28) Steimle, T. C.; Robinson, J. S.; Goodridge, D. J. Chem. Phys. 1999,
110, 881.
(35) Brown, J. M.; Cheung, A. S-C.; Merer, A. J. J. Mol. Spectrosc.
1987, 124, 464.
(29) Ram, R. S.; Bernath, P. F.; Davis, S. P. J. Mol. Spectrosc. 2001,
210, 110.
(30) Ram, R. S.; Bernath, P. F.; Davis, S. P. J. Mol. Spectrosc. 2002,
215, 163.
(31) Scherer, J. J.; Paul, J. B.; O’Keefe, A.; Saykally, R. J. Chem. ReV.
1997, 97, 25.
(32) Ma, T.; Leung, J. W-H.; Cheung, A. S-C. Chem. Phys. Lett. 2004,
385, 259.
(36) Bauschlicher, C. W.; Bagus, P. S.; Nelin, C. J. Chem. Phys. Lett.
1983, 101, 229.
(37) Sennesal, J. M.; Schamps, J. Chem. Phys. 1987, 114, 37.
(38) Langhoff, S. R. Astrophys. J. 1977, 481, 1007.
(39) Lefebvre-Brion, H.; Field, R. W. Perturbations in the Spectra of
Diatomic Molecules; Academic Press: New York, 1986.
(40) Simard, B.; Mitchell, S. A.; Humphires, M. R.; Hackett, P. A. J.
Mol. Spectrosc. 1988, 129, 189.
(33) Edlen, B. Metrologia 1966, 2, 71.
(34) Brown, J. M.; Kopp, I.; Malmberg, C.; Rydh, B. Phys. Ser. 1978,
17, 55.
(41) Kappes, M. M. Chem. ReV. 1988, 88, 369.