A new (multi-reference configuration interaction) potential energy surface for H 2 CO and preliminary studies of roaming

Abstract

We report a new global potential energy surface (PES) for H 2 CO, based on precise fitting of roughly 67 000 MRCI/cc-pVTZ energies. This PES describes the global minimum, the cis - and trans -HCOH isomers, and barriers relevant to isomerization, formation of the molecular (H 2 +CO) and radical (H+HCO) products, and the loose so-called roaming transition-state saddle point. The key features of the PES are reviewed and compared with a previous PES, denoted by PES04, based on five local fits that are ‘stitched’ together by switching functions (Zhang et al. 2004 J. Phys. Chem. A 108 , 8980–8986 ( doi:10.1021/jp048339l )). Preliminary quasi-classical trajectory calculations are performed at the total energy of 36 233 cm −1 (103 kcal mol −1 ), relative to the H 2 CO global minimum, using the new PES, with a particular focus on roaming dynamics. When compared with the results from PES04, the new PES findings show similar rotational distributions, somewhat more roaming and substantially higher H 2 vibrational excitation. This article is part of the themed issue ‘Theoretical and computational studies of non-equilibrium and non-statistical dynamics in the gas phase, in the condensed phase and at interfaces’.