Vibrational state control of HPCO photodissociation in the S1 band

Abstract

Control of molecular photodissociation process is expected to be achieved owing to its relatively fast and direct dynamics that fulfill the criteria to achieve mode specificity in chemical reactions. HPCO is a typical tetra-atomic system with different atoms, which may have an obvious mode-specific character in its photodissociation process HPCO(S1) → H + PCO/HP + CO. In this work, the control of the photodissociation dynamics of HPCO was investigated by both the quantum mechanical (QM) and quasi-classical trajectory (QCT) dynamical methods, in which a scheme of vibrational excitation for the initial state was utilized. By and large, the QM and QCT results are reasonably consistent and some energy-dependent differences caused by quantum effects exist. It was found that the excitation of the H–P stretching (v1) mode promotes the yield of the product H + PCO to the greatest extent. While, for the HP + CO channel, the excitation of the C–O stretching (v2) mode was found to promote the production of HP + CO more efficiently than the P–C stretching (v4) mode, stemming from the bottleneck in the exit channel and intramolecular vibrational energy redistribution caused by the relatively long-lived resonances in the wells on the S1 potential energy surface. Simultaneously, the photon energy is found to greatly affect the quantum yield of H + PCO due to the asymptote of the product HP + CO ∼ 1.0 eV lower than that of the product H + PCO in energy, as well as large differences between the frequencies of the H–P stretching and P–C stretching modes.