ION IMAGING OF THE PHOTODISSOCIATION OF OCS NEAR 217 AND 230 NM

OCS was photodissociated near 217 and 230 nm, and the resulting CO was probed by 2 + 1 resonant multiphoton ionization (REMPI) using the B-1 Sigma(+), C-1 Sigma(+) <--<-- X(1) Sigma(+) transitions. The CO+ was detected by the ion imaging technique of Chandler and Houston. The nas cent CO was found only in the v = 0 state, and its rotational state po pulation distribution was bimodal. It is remarkable that this CO rotat ional distribution has no tail extending to states of lower J. beta va lues rise monotonically with J. Recent potential energy surface calcul ations by Rokutan et al. provide reasonable explanations for the resul ts: (1) dissociation can take place from near degenerate A '' and A' s tates, each of which generates a different CO product distribution; (2 ) a molecule excited by the initial absorption to an A' state can cros s over in linear geometry at two different C-S distances to dissociati ng states.