Direct ab initio molecular dynamics study of the two photodissociation channels of formic acid

Kurosaki, Yuzuru; Yokoyama, Keiichi  ; Teranishi, Yoshiaki

A total of 1200 trajectories have been integrated for the two dissociation channels of formic acid, HCOOH HO + CO (1) and HCOOH CO + H (2), which occur with 248 and 193 nm photons, using the direct ab initio molecular dynamics method at the RMP2(full)/cc-pVDZ level of theory. It was found that the percentage of the energy distributed to a relative translational mode in reaction 2 is much larger than that in reaction 1. This is mainly due to the difference in the geometry of transition state (TS); the HO geometry in the TS of reaction 1 was predicted to significantly deviate from the equilibrium one, whereas the CO and H geometries in the TS of reaction 2 were found to be more similar to their equilibrium ones. It was also found that the product diatomic molecules, CO and H, are both vibrationally and rotationally excited. The calculated relative population of the vibrationally excited CO for the 248 nm photodissociation was consistent with experiment.