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

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 – 0.95 ns247 – 38 ns – 4.61 ps35 – 24 ns 2~ 1 ps2.31 ps SH A 2  + - X 2  (1,0)

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

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)

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)

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

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 ) (9) 0.07 (3) 0.80 (12) (4) 0.06 (2) 0.76 (5) (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)

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

Anisotropy parameters (  v ) # P.L. Houston et al., J. Chem. Phys. 125, (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)

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)

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

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.

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.

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