TRANSITION-STATE DYNAMICS OF O(P-3)-SIMILAR-TO-85 KJ MOL(-1)(OCS, CS2REACTIVE SCATTERING AT INITIAL TRANSLATIONAL ENERGY E)

Reactive scattering of ground state O(P-3) atoms with OCS and CS2 mole cules has been studied at an initial translational energy E similar to 85 kJ mol(-1) using a supersonic beam of O atoms seeded in He buffer gas generated from a high temperature radio frequency discharge source . The center-of-mass angular distribution of SO scattering for O + OCS is cone shaped peaking at a scattering angle theta similar to 70 degr ees with respect to the incident O atom direction, while that for O CS2 peaks sharply in the forward direction theta = 0 degrees. A simila r fraction f' similar to 0.3 of the total available energy is disposed into product translation for each reaction despite the substantial di fference in exoergicities. The cone shaped scattering for O + OCS, ari ses from direct dissociation of the early transition state which is fo rmed by broadside approach of the O atom to the S atom of the OCS mole cule. The sideways recoil of the SO product is carried into the forwar d hemisphere by the initial momentum of the O atom. The forward peaked scattering for O + CS2 arises from the precession of a weakly bound O SCS intermediate with a lifetime of one-third of a rotational period. In both cases reaction occurs over a (3)A '' potential energy surface involving planar bent cis or trans intermediates with bending mode exc itation resulting in high product rotational excitation.