Characterizing the photodissociation dynamics of HPCO in the S1 band

A full-dimensional potential energy surface (PES) represented by the neural network method for the first excited state S1(1A″) of HPCO is reported for the first time. The PES was constructed based on more than 51 000 ab initio points, which were calculated at the multi-reference configuration interaction level with Davidson correction using the augmented correlation consistent polarized valence triple zeta basis set. Based on the newly constructed PES, quasi-classical trajectory calculations were carried out to study the photodissociation dynamics of HPCO at the total energy ranging from 4.0 to 5.6 eV. At low total energies, the HP + CO product is dominant, while the product H + PCO becomes increasingly favored at higher energies. Furthermore, the translational energy distributions of two products are found to be energy-dependent. Owing to the strongly repulsive PES along the HP + CO dissociation pathway, the translational energy distributions of HP + CO are dominated by relatively higher energies in contrast to H + PCO. The diatomic products HP and CO are found to possess the vibrational distributions decaying monotonically with the vibrational quantum number and relatively cold rotational state distributions, consistent with the strongly repulsive potentials toward the HP + CO channel. In addition, the vibrational distributions of HP and CO are found to be quite similar due to their close frequencies, while the rotational distributions of CO have a much more highly excited rotational degree of freedom owing to its rotational constant approximately four times smaller than that of HP.