Photoexcitation and charge-transfer-to-solvent relaxation dynamics of the I(-)(CH3CN) complex

Photoexcitation of iodide-acetonitrile clusters, I(-)(CH3CN)n, to the charge-transfer-to-solvent (CTTS) state and subsequent cluster relaxation could result in the possible formation of cluster analogues of the bulk solvated electron. In this work, the relaxation process of the CTTS excited iodide-acetonitrile binary complex, [I(-)(CH3CN)]*, is investigated using rigorous ab initio quantum chemistry calculations and direct-dynamics simulations to gain insight into the role and motion of iodine and acetonitrile in the relaxation of CTTS excited I(-)(CH3CN)n. Computed potential energy curves and profiles of the excited electron vertical detachment energy for [I(-)(CH3CN)]* along the iodine-acetonitrile distance coordinate reveal for the first time significant dispersion effects between iodine and the excited electron, which can have a significant stabilizing effect on the latter. Results of direct-dynamics simulations demonstrate that [I(-)(CH3CN)]* undergoes dissociation to iodine and acetonitrile fragments, resulting in decreased stability of the excited electron. The present work provides strong evidence of solvent translational motion and iodine ejection as key aspects of the early time relaxation of CTTS excited I(-)(CH3CN)n that can also have a substantial impact on the subsequent electron solvation processes and further demonstrates that intricate details of the relaxation process of CTTS excited iodide-polar solvent molecule clusters make it heavily solvent-dependent.