Photodissociation of van der Waals complexes of iodine X-I (X = I, CH) via charge-transfer state: A velocity map imaging investigation.

The photodissociation of van der Waals complexes of iodine X-I (X = I, CH) excited via Charge-Transfer (CT) band has been studied with the velocity map imaging technique. Photodissociation of both complexes gives rise to translationally "hot" molecular iodine I via channels differing by kinetic energy and angular distribution of the recoil directions. These measured characteristics together with the analysis of the model potential energy surface for these complexes allow us to infer the back-electron-transfer (BET) in the CT state to be a source of observed photodissociation channels and to make conclusions on the location of conical intersections where the BET process takes place. The BET process is concluded to provide an I molecule in the electronic ground state with moderate vibrational excitation as well as X molecule in the electronic excited state. In the case of X = I, the BET process converts anion I of the CT state into the neutral I in the repulsive excited electronic state which then dissociates promptly giving rise to a pair of I atoms in the fine states P. In the case of CH-I, the CH molecules appear in the triplet T electronic state. Conical intersection for corresponding BET process becomes energetically accessible after partial twisting of CH frame in the excited CT state of complex. The CH(T)-I complex gives rise to triplet ethylene as well as singlet ethylene via the T-S conversion.