Ultraviolet photolysis of formyl fluoride: the F+HCO product channel

Abstract

The time-of-flight spectrum of the H atoms resulting from photodissociation of gas phase HFCO molecules at 243.12 nm indicates a role for secondary photolysis of HCO() fragments arising via the F+HCO() dissociation channel. Analysis of this spectrum, and of earlier photofragment translational spectroscopy results obtained at a number of neighbouring wavelengths in the range 218.4–248.2 nm, allow estimation of an upper limit for the C–F bond dissociation energy: D₀(F–CHO)⩽482 kJ mol^-1. HCO() fragments are deduced to be amongst the primary products of HFCO photolysis at all wavelengths λ⩽248.2 nm, indicating that any energy barrier in the F–C bond fission channel [measured relative to the asymptotic products F(²P)+HCO()] must be small. This observation is considered in the light of available knowledge regarding the potential energy surfaces for the ground (¹A′) and first excited singlet (ùA″) and triplet (ã³A″) states of HFCO; the available evidence all points to radiationless transfer and subsequent dissociation on the triplet surface as the mechanism for the deduced F–C bond fission.