Formyl fluoride photodissociation: Potential energy surface features of singlet HFCO

The unimolecular dissociation of formyl fluoride to hydrogen fluoride and carbon monoxide and its unimolecular rearrangement to fluorohydroxymethylene have been examined theoretically. Methods ranged from double zeta plus polarization self-consistent-field to triple zeta plus double polarization coupled cluster singles and doubles. The coupled cluster method including single, double, and linearized triple excitations (CCSDT-1) was applied as well with the double zeta plus polarization basis. The present studies predict a barrier height of ∼47 kcal mol−1 to the molecular dissociation which is ∼11 kcal mol−1 lower than previous theoretical work and in reasonable agreement with experiments that indicate this barrier lies in the range 40 to 43 kcal mol−1. The existence of singlet trans- and cis-fluorohydroxymethylenes at ∼43 kcal mol−1 above formyl fluoride is further confirmed theoretically. The 1,2-hydrogen shift transition state connecting formyl fluoride to the trans-fluorohydroxymethylene lies at ∼77 kcal mol−1. The trans- and cis-fluorohydroxymethylenes are separated by an internal rotation barrier of ∼17 kcal mol−1.