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’.