ROLE OF INTERSYSTEM CROSSING IN THE REACTIVE SCATTERING OF O(P-3) ATOMS WITH CH2I2 MOLECULES

Reactive scattering of O(P-3) atoms with CH2I2 molecules has been meas ured at initial translational energies E approximate to 48 and 15 kJ m ol(-1) using a supersonic beam of O atoms seeded in He and Ne buffer g ases generated from a high-pressure microwave discharge source. At bot h initial translational energies the angular distribution of IO scatte ring is mildly forward and backward peaked, slightly favouring the bac kward direction. Both product translational energy distributions peak at low energy with a long tail extending out to higher energy. Compari son with the predictions of phase space theory indicates that the IO p roduct scattering arises mainly from long-lived collision complex dyna mics following intersystem crossing from the initial triplet to the un derlying singlet potential-energy surface, while a small contribution also arises from direct dynamics in IO scattering over a wide angular range with higher product translational energy. This pattern of behavi our is related to the structures of the reaction intermediates on both the singlet and triplet potential-energy surfaces.