1. Predissociation of the A 2  + state of the SH (SD) radical A.J. Orr-Ewing, R.A. Rose, C.-H. Yang, K. Vidma and D.H. Parker

2. Spectroscopic studies of SH(A 2  + ) A 2  + (v,J) lifetimes for SH and SD from LIF (Ubachs et al., Kawasaki et al.) and CRDS (Wheeler et al.) M.D. Wheeler et al. J. Chem. Phys. 107, 7591 (1997) Lifetime v'SHSD 03.20 – 0.95 ns247 – 38 ns 15.45 – 4.61 ps35 – 24 ns 2~ 1 ps2.31 ps SH A 2  + - X 2  (1,0)

3. Predissociation of the A 2  + state Lifetimes modelled using Fermi Golden Rule calculations Fitted A-state and ab initio repulsive potentials

4. Dissociation dynamics Is dissociation adiabatic or non-adiabatic on the repulsive PE curves? Asymptotic measurements of: S( 3 P J ) spin-orbit branching ratios m-state populations recoil velocity anisotropy (  parameters) Velocity map imaging of S( 3 P J ) photofragments H-atom PTS (Jingsong Zhang, UC Riverside)

5. Velocity map imaging Field free TOF Pulsed nozzle & discharge Ion optics Nd:YAG Dye laser KDP crystal MCPs P47 CCD camera 25% H 2 S (D 2 S)/ Xe Photolysis laser Probe S( 3 P J ) by 2+1 REMPI Nd:YAG KDP crystal Dye laser H V H V SH(X 2  ; v=0, j)  SH(A 2  + ; v', j')  S( 3 P J ) + H( 2 S) SH(A 2  + v'=0, 1 & 2) via P 1 (1.5), Q 1 (1.5) and R 1 (1.5) + R Q 21 (1.5)

6. Information in velocity images r Radius is proportional to S atom speed Image intensity depends on the number of S( 3 P J ) atom products Angular distributions give information on the recoil velocity direction and the alignment of angular momentum of S( 3 P) atoms

7. S( 3 P J ) branching – nonadiabatic dynamics SH(A,v’=1) S( 3 P 0 )S( 3 P 1 )S( 3 P 2 ) v'=0 SH v'=1 v'=2 A 2  + v' S( 3 P 0 )S( 3 P 1 )S( 3 P 2 ) 00.13 (9) 0.07 (3) 0.80 (12) 10.18 (4) 0.06 (2) 0.76 (5) 20.34 (5) 0.04 (2) 0.62 (7)     1/2 3/2 5/2 H( 2 S) + S( 3 P 0 ) H( 2 S) + S( 3 P 1 ) H( 2 S) + S( 3 P 2 )  Repulsive PE curves X-state  A-state 1/2 H( 2 S) + S( 1 D)

8. Angular anisotropy in the images S( 3 P 0 ) V V H S( 3 P 2 ) J = 0 so no alignment

9. Anisotropy parameters (  v ) # P.L. Houston et al., J. Chem. Phys. 125, 133316 (2006) For predissociative states, velocity anisotropy is reduced by rotation of molecule – depends on lifetime and interference between overlapping transitions. # SH A 2  + - X 2  v' = 2  v'' = 0 P 1 (1.5) Q 1 (1.5) R 1 (1.5)

10. Hyperfine depolarization Nuclear spin coupling can depolarize bond alignment; Hyperfine coupling timescales are a few ns; Anisotropy parameters for SH/SD A 2  + v=0 reduced. Lifetime for SH(A,v=0, J=1.5) Q 1 (1.5)

11. Angular momentum polarization Analysis of probe laser polarization dependence of angular anisotropy of images; Populations of m-states for S( 3 P 2 ) and S( 3 P 1 ). 3P13P1 3P23P2

12. m-state correlations 4  - 1/2  S( 3 P 2 m =  1) + H( 2 S 1/2 m = ½) 2  1/2  S( 3 P 2 m = 0) + H( 2 S 1/2 m =  ½) Non-adiabatic transitions between 4  - 1/2 and X 2  1/2 state at long range, mediated by spin-orbit coupling.  = 3/2 states correlate to S( 3 P 2 m =  2); requires rotation-induced couplings.

13. Conclusions Predissociation of the low v' levels of the A 2  + state of SH and SD is via coupling to the 4  - state; Lifetimes (measured by LIF and CRDS) affect the photofragment recoil velocity anisotropy;  values are successfully modelled by theory; Hyperfine couplings can degrade the anisotropy; S( 3 P J ) branching ratios and m-state populations indicate non-adiabatic dissociation dynamics from the 4  - 1/2 state to the X 2  1/2 and 4  1/2 states.

14. Acknowledgements Rebecca RoseDavid Parker Chung-Hsin Yang Konstantin Vidma Gerrit Groenenboom