June 18, 2007 62 nd Symp. on Molec. Spectrosc. The Pure Rotational Spectra of VN (X 3 r ) and VO (X...

June 18, 200762nd Symp. on Molec. Spectrosc.

The Pure Rotational Spectra of VN (X 3r) and VO (X 4-):

A Study of the Hyperfine Interactions

Michael A. Flory

and

Lucy M. Ziurys

Department of Chemistry

Steward Observatory

University of Arizona


Motivations for High Resolution Vanadium Spectroscopy

• V-containing compounds frequently being found as air and ground pollutants in Europe, Asia, and South America

• Astronomy– VO electronic spectrum identified in O-rich

stars– VN-type compounds recently detected in

comets

• Understanding of bonding properties• Relatively few V radicals studied (VN,

VO, VF, VCl, VCl+, VS, VCH)• Interesting hyperfine structures from

vanadium nuclear spin (I = 7/2)


• Radiation Source: Phase-locked Gunn oscillators and Schottky diode multipliers (65-660 GHz)

• Gaussian beam optics utilized to minimize radiation loss

• Reaction Chamber: Double walled, glass cell cooled by methanol with 2 ring electrodes

• Detector: InSb bolometer

• Radiation is modulated at 25kHz and detected at 2f

Submillimeter Spectroscopy


• Most 3d transition metals melt in Broida oven• Vanadium not possible using current oven

technology (m.p. > 1900 °C)• Use new velocity modulation spectrometer• Testing reactivity of VCl4 (l) – high v.p.• VN:

– VCl4 (1 mTorr)– N2 (3-5 mTorr)– Ar (20 mTorr)

• VO:– VCl4 (1 mTorr)– Residual water– Ar (20 mTorr)

• 250 W AC discharge• Deep purple glow from V emission

Molecular Synthesis


VN (X 3r) Background• Quantum mechanics

– S = 1, = 2– Hund’s case (a) coupling – R + L + S = J– 3 fine structure components ( = 1, 2, 3)– Hyperfine octets from V nucleus (I = 7/2)

J

J+I=F

= 1

= 3

= 2

• Previous work:– Ram et al. have studied many excited states– Balfour et al. (J. Chem. Phys., 1999) examined D 3 – X 3

• Both states are perturbed• X 3 interacts with 1 state• D 3 perturbed by d 1 and e 1 states

– Established rotational and fine structure parameters– Determined h1, h2, h3 hyperfine constants


VN Spectra• Transitions usually within 20

MHz of frequencies calculated using Balfour et al.

• Nice Landé pattern

• Intensity F

• F assignment reverse in = 1 from = 2, 3

• Wide range of h.f. spacing

• No -doubling observed

• No Nitrogen hyperfine (I = 1)


VN Results

MHz• 7 rotational transitions recorded in range 297 – 528 GHz

• 157 lines measured


VN Analysis• Hund’s case (a) effective Hamiltonian

Heff = Hrot + Hso + Hss + Hmhf + HeqQ

• Only ONE state to fit (X 3)

• Frosch and Foley hf terms fit (a, b, b+c)

• The = 2 component is perturbed by 1• Third-order spin-orbit/Fermi contact

cross term

• Manifests as correction to a

• Included “deperturbation term”, a

<=2|Hmhf|=2> = 2a + a

• Estimate energy to excited 1 state

MHz Present Work Balfour et al.

B 18 747.557 4(12) 18 746.88(18)

D 0.027 834 2(36) 0.027 29(31)

A 2 249 700(2 900) 2 263 552(29)

AD -1.53(10) -0.763(27)

188 500(1 100) 101 026.6(3.0)

D 9.34(13) -0.387(28)

H 0.000 296 9(65)

a 338.80(30)

a 147.32(74)

b 1 350.8(2.9)

b+c 1 253.99(55)

(b+c)D 0.203(10)

eqQ 15.9(2.3)

h1 1 940.3(8.4)

h0 827.1(6.6)

h-1 -586.4(9.0)

b+ 1 321(83)

b- 1 404(57)

rms 0.023 138

131

3099)(

)(4

cm

E

cbAa


VO (X 4-) Background• Quantum mechanics

– S = 3/2, = 0– Hund’s case (b) coupling – N + S = J– 4 fine structure components, closely

spaced– Hyperfine octets from V nucleus (I = 7/2)

N

J+I=F

F1

F2

F3

F4

N+S=J

• Previous work:– Many electronic transitions investigated– Richards and Barrow examined internal hyperfine perturbation in

X 4- (1968)– Suenram et al. measured 3 transitions of FTMW spectrum at 8

GHz– Adam et al. combined FTMW with optical data for ground state

(1995)


VO (X 4-) Spectra• Transitions usually within 5-10

MHz of frequencies calculated using Adam et al.

• NO traditional patterns for V octets

• Dramatically varying widths in h.f. spacing

• Form “band-heads”

• Internal hyperfine perturbation to F2 and F3

N = 0, J = 1, F = 0– Basis set breaks down and

quantum numbers difficult to assign in Hamiltonian

• F1 and F4 due to matrix elements

– No difficulty in assigning or fitting transitions

F4

F3

F2

F1


VO (X 4-) ResultsMHz F4 (J″ = N″ – 3/2)b F3 (J″ = N″ – 1/2) F2 (J″ = N″ + 1/2)

N′ F′ N″ F″ obs-calc F′ F″ obs-calc F′ F″ obs-calc

9 4 8 3 291860.801 0.172 5 4 293722.745 0.024 6 5 296266.224 -0.070

5 4 291780.859 0.030 6 5 293739.109 -0.011 7 6 296245.767 -0.041

6 5 291716.282 0.035 7 6 293750.243 -0.007 8 7 296225.376 -0.026

7 6 291666.659 0.066 8 7 293755.008 -0.031 9 8 296206.913 -0.007

8 7 291631.483 0.028 9 8 293752.100 -0.018 10 9 296193.378 0.026

9 8 291610.349 0.039 10 9 293739.109 0.023 11 10 296190.751 0.134

10 9 291602.584 0.058 11 10 293710.752 0.028 12 11 296212.942 -0.027

11 10 291607.419 0.025 12 11 293653.630 0.054 13 12 296305.960 -0.040

10 5 9 4 325054.643 0.038 6 5 326577.527 -0.005 7 6 328762.810 -0.003

6 5 324991.938 0.000 7 6 326606.107 -0.046 8 7 328730.692 -0.052

7 6 324942.315 -0.003 8 7 326629.529 -0.048 9 8 328700.203 0.018

8 7 324905.508 -0.009 9 8 326646.815 -0.039 10 9 328672.780 -0.020

9 8 324881.189 -0.040 10 9 326656.753 0.059 11 10 328651.530 -0.034

10 9 324868.951 -0.136a 11 10 326656.653 0.074 12 11 328643.093 -0.043

11 10 324868.751 0.096 12 11 326640.405 0.024 13 12 328666.370 -0.024

12 11 324879.438 0.006 13 12 326589.827 0.003 14 13 328802.908 -0.041

• 7 rotational transitions recorded in range 291 – 525 GHz


VO

MHz MM-wave Adam et al.

B 16 379.618 6(14) 16 379.798(17)

D 0.019 363 8(39) 0.019 460 0(96)

672.168(39) 672.328(42)

D 0.001 970(75) 0.001 80(68)

s 0.220 4(81) 0.243(95)

60 881.03(55) 60 884.97(45)

D 0.018 16(61) 0.011 5(48)

bF 778.737(66) 777.54(15)

c -129.84(19) -134.83(46)

cI 0.192 8(51)

bs -0.660(14) -0.472(37)

eqQ -2.5(1.3) 40.17(48)

rms 0.052 11

VO Analysis

• Combined sub-mm with FTMW data

• Hund’s case (b) effective HamiltonianHeff = Hrot + Hss + Hmhf + HeqQ

• Higher order terms required– bs = Third-order spin-orbit distortion to

Fermi contact when S > 1

– s = Third-order spin-rotation

• Generally good agreement with previous values

• Better predictions of sub-millimeter frequencies


Conclusions

• Measured pure rotational spectra of VO and VN

• Established global fit of hyperfine constants in VN ground state

• Both radicals exhibit interesting perturbations to the hyperfine structure

• VCl4 is a possible V source for additional radical synthesis in the future (VC, VNC, VOH, …)


Thanks to…

Lucy Ziurys

Ziurys GroupDr. Aldo ApponiDr. DeWayne HalfenStefanie Milam, Emmy Tenenbaum, Robin Pulliam,

Ming Sun

FundingNSFNASA Laboratory Astrophysics

June 18, 2007 62 nd Symp. on Molec. Spectrosc. The Pure Rotational Spectra of VN (X 3 r ) and VO (X...

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Transcript of June 18, 2007 62 nd Symp. on Molec. Spectrosc. The Pure Rotational Spectra of VN (X 3 r ) and VO (X...