ROLE OF INTERSYSTEM CROSSING IN THE REACTIVE SCATTERING OF O(P-3) ATOMS WITH CF3CH2I MOLECULES

Reactive scattering of O(P-3) atoms with CF3CH2I molecules has been me asured at initial translational energies E approximate to 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 b oth initial translational energies the observed IO product scattering is found to be compatible with reaction via a long-lived collision com plex. This is attributed to intersystem crossing from the initial trip let potential energy surface to the underlying singlet potential energ y surface that supports a stable OICH2CF3 intermediate. However, the a ngular distribution of IO scattering at higher initial translational e nergy shows a mild preference for backward scattering, which is attrib uted to a small fraction of direct reaction dynamics over the triplet potential energy surface. No scattering of HOI reaction product is obs erved as this reaction pathway requires abstraction of a terminal H at om via a five-membered ring transition state and this is inhibited for the singlet OICH2CF3 intermediate by the fluorination of the terminal CF3 group.