Role of intersystem crossing in the reactive scattering of O(3P)atoms with CF3CH2Imolecules

Abstract

Reactive scattering of O(³P) atoms with CF₃CH₂I molecules has been measured at initial translational energies E≈45 and 16 kJ mol^-1 using a supersonic beam of O atoms seeded in He and Ne buffer gases generated from a high pressure microwave discharge source. At both initial translational energies the observed IO product scattering is found to be compatible with reaction via a long-lived collision complex. This is attributed to intersystem crossing from the initial triplet potential energy surface to the underlying singlet potential energy surface that supports a stable OICH₂CF₃ intermediate. However, the angular distribution of IO scattering at higher initial translational energy shows a mild preference for backward scattering, which is attributed to a small fraction of direct reaction dynamics over the triplet potential energy surface. No scattering of HOI reaction product is observed as this reaction pathway requires abstraction of a terminal H atom via a five-membered ring transition state and this is inhibited for the singlet OICH₂CF₃ intermediate by the fluorination of the terminal CF₃ group.