1. Perturbations of the Fine and Hyperfine Structure in the Pure Rotational Spectrum of VCl (X5Dr)
DeWayne T. Halfen and Lucy M. Ziurys
Department of Chemistry
Department of Astronomy
Steward Observatory
Arizona Radio Observatory
University of Arizona
June 21, 2004

2. Why VCl ? Few vanadium compounds studied at high resolution
Optical studies of VH, VO, VN, VF, VCl
Only pure rotational spectra of any vanadium compound
Microwave spectrum of VO (X4S-1/2) from 3-11 GHz (Suenram et al. 1991)
Vanadium – many oxidation states
Bonding trends across periodic table
High melting point
~1900oC – can’t melt in Broida oven
Laser ablation
VOCl3 (l) or VCl4 (l)
V oxidation states

3. Past Work on VCl Iacocca et al. (1970) first observed visible spectrum
No ground state determined
Ram, Bernath & Davis (2001) & Ram et al. (2003)
Measured several subbands of E5D-X5D transition
Identified the W = 1,2,3,4 subbands, but couldn’t resolve W = 0
Subbands not regularly spaced
ab initio calculations showed a 5P state very close in energy to ground state
Perturb the ground state W = 0,1,2,3 subbands

5. Gas-Phase Synthesis of VCl
Add VCl4
Pressure: 1-2 mTorr
20 mTorr Ar gas also added
AC discharge
200 W at 600 W

6. Energy Level Diagram for VCl (X5Dr)
5Dr ground state
Four unpaired 3d electrons
J = L + S
Spin-orbit and spin-spin interactions
Omega ladders
W = 0, 1, 2, 3, 4
J ≥ W
Lambda-doubling possible
Vanadium hyperfine
I(51V)= 7/2
F = J + I
80 lines max. per transition J W 3 4 2 1
X5Dr J F W
J+3/2
J+1/2
J+7/2
J+5/2
J-5/2
J-7/2
J-1/2
J-3/2

7. V35Cl: J = 37  38
Pattern repeats
in V37Cl

8. V35Cl: J = 37  38

9. Rotational Spectrum of VCl
V35Cl (X5Dr) J = 37  38
W = 4
Lambda doubling
collapsed *
W = 3
W = 1
W = 2
Vanadium Hyperfine
W = 0
Lambda Doubling
Measured 10 rotational transitions of V35Cl and V37Cl

10. For more data, see Halfen & Ziurys 2005 J′ F′ J″ F″ nobs no-nc W = 0f
W = 0e
W = 3f
W = 3e 33
30.5 32
29.5
0.318
0.260
-0.011
0.019
31.5
0.315
0.236
0.037
0.013
32.5
0.213
0.180
-0.013
-0.008
33.5
0.077
0.065
0.027
-0.033
34.5
-0.195
-0.132
-0.021
-0.018
35.5
-0.625
-0.423
-0.022
36.5
-1.159
-0.831
-0.014
-0.017
W = 1f
W = 1e
W = 4
28.5
-0.201
-0.026
0.015
-0.113
-0.047
-0.004
-0.099
-0.005
0.006
-0.029
0.029
0.005
0.049
0.026
0.066
0.009
-0.002
0.096
-0.019
-0.023
-0.165
0.000
W = 2f
W = 2e
-0.192
-0.393
-0.563
-0.260
-0.670
-0.039
-0.555
0.085
-0.220
0.562
0.242
0.708
0.853
0.785
1.532
0.611
For more data, see
Halfen & Ziurys 2005

11. Hyperfine Perturbations1 2
3,4 5
6 7 8
Hyperfine Perturbations
Hyperfine splittings in W = 1
Octets at lower frequencies
3 to 4 lines at higher frequencies
For W = 1e, at J = 38  39 and J = 39  40, hyperfine spreads out to over MHz
Hyperfine splittings in W = 2
Regular octets for both lambda doublets
At J = 39  40 & J = 40  41, hf spreads out over 100 MHz for W = 2e only
Evidence for perturbing state at very low energy
W = 2
W = 1e

12. Spectroscopic Analysis of VCl
Hund’s case (c) scheme
Each individual W component fit separately – Heff = Hrot + Hmhf
Rotational constants agree well with Ram et al. (2003)
h parameter doesn’t follow regular pattern – h = aL + (b+c)S
Higher-order distortion constants, hH, needed for good fit ^ ^ ^ W B D H h hD hH
rms 0f
(73)
(51)
-1.88(12)E-07
4346(650)
7.06(12)
(42)
0.313 0e
(52)
(37)
-1.091(85)E-07
3959(523)
6.08(10)
(34)
0.225 1f
(36)
(17)
276(89)
-1.10(20)
(53)
0.070 1e
(91)
(11)
2.288(41)E-07
354(67)
-2.06(13)
(34)
0.046 2f
(20)
(79)
4302(289)
4.82(37)
(22)
0.613 2e
(35)
(15)
-6.33E-08b
4439(353)
4.58(55)
(28)
0.637 3f
(76)
(53)
1.22(12)E-08
437(31)
-0.338(45)
(58)
0.032 3e
(15)
(11)
-5.24(25)E-09
456(28)
-0.326(19)
0.067 4
(48)
(14)
835.9(8.6)
-0.259(12)
(16)
0.012
a In MHz. b Held Fixed.

13. Source of Hyperfine Perturbations
A5Pr state perturbs W = 0, 1, 2, 3 components (DW = 0)
Homogeneous spin-electronic perturbation
W = 1 perturbed most
A5P11/2mr2 L±S X5D1
f parity L-doubling components shifted lower in energy
Nearby B5S- state (Ram et al. 2003)
e parity components shifted to higher energy
A5Pr state only ~500 cm-1 higher than X5Dr
W = 1e & 2e components strongly interact
Second-order spin-orbit/Fermi-contact cross term (L S)(I S) . .

14. Future Work Refine global case (a) fit for VCl Deperturbation analysis
Aso = 1226 GHz = 41 cm-1
rms = 1.3 MHz w/o W = 1
Deperturbation analysis
Measure spectra of more vanadium species
VF (X5Dr or X5Pr)
VO (X4S-)
VN (X3Dr)
VH (X5Dr)