Reactive scattering of ground state O(3P) atoms with OCS and CSz molecules has been studied at an initial translational energy E -85 kJ mol-' using a supersonic beam of 0 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 0 + OCS is cone shaped peaking at a scattering angle 8 -70' with respect to the incident 0 atom direction, while that for 0 + CS2 peaks sharply in the forward direction 8 = 0". A similar fractionf' -0.3 of the total available energy is disposed into product translation for each reaction despite the substantial difference in exoergicities. The cone shaped scattering for 0 + OCS arises from direct dissociation of the early transition state which is formed by broadside approach of the 0 atom to the S atom of the OCS molecule. The sideways recoil of the SO product is carried into the forward hemisphere by the initial momentum of the 0 atom. The forward peaked scattering for 0 + CS2 arises from the precession of a weakly bound OSCS intermediate with a lifetime of one-third of a rotational period. In both cases reaction occurs over a 3A" potential energy surface involving planar bent cis or trans intermediates with bending mode excitation resulting in high product rotational excitation.
Reactive scattering of O(3P) atoms with Br2 and Cl2 molecules has been studied at an initial translational energy E -90 kJ mol-' using a supersonic beam of 0 atoms seeded in He buffer gas generated from a high-temperature radio-frequency discharge source. The center-of-mass angular distribution of BrO scattering is cone-shaped, peaking at a scattering angle 8 -95" with respect to the incident 0 atom direction, while that for C10 peaks sharply in the forward direction with a subsidiary backward peak of relative intensity -0.5. The 0 + Br2 reaction disposes a substantial fractionf' -0.4 of the total available energy into product translation, while the product translational energy distribution for 0 + C12 peaks at low energy f ' -0.13 with a long tail extending to higher energy. The 0 + Br2 scattering is attributed to direct dissociation of a mildly bent OBrBr transition state at the top of a barrier on the 3A" potential energy surface. This contrasts with the long-lived complex dynamics observed for 0 + Br2 at low initial translational energy which is now attributed to intersystem crossing to the underlying 'A' potential energy surface followed by dissociation of a stable bent BrOBr complex. However, the short-lived collision complex dynamics observed for 0 + C12 continues the behavior observed at lower initial translational energy. The absence of direct scattering for 0 + Cl2 is attributed to a higher potential energy barrier on the 3A" potential energy surface than for 0 + Br2, while the continuation of intersystem crossing to the 'A' surface is attributed to the seam of singlet-triplet intersection occumng at smaller internuclear distance, resulting in stronger spin-orbit interaction and stronger forces leading to the bent ClOCl complex.
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