Ultraviolet photolysis of formyl fluoride: the F+HCO product channel
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 (Ã1A″) 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.