The vacuum-ultraviolet photolysis of the difluoroethylenes

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Abstract
The vacuum‐ultraviolet (vuv) photochemistry of the various isomeric difluoroethylenes has been investigated in argon and carbon monoxide matrices at 10 and 24 K. Selective excitation at various frequencies of the broad π*←π absorptions with N and Br resonance line sources results in two major processes and additional minor processes based on infrared intensities. As major processes, all three difluoroethylenes photodissociate into fluoroacetylene (FA) and HF via molecular elimination, and all give rise to to the same free radical C2HF2, presumably via atomic detachment. No acetylene (A) or difluoroacetylene was observed. Isomerization of the three difluoroethylenes into each other was observed as the minor processes. The results of experiments conducted in CO matrices, wherein almost total quenching of the atomic detachment process and normal occurrence of molecular elimination were observed, strongly suggest that the former occurs via intersystem crossing (ISC) and the latter via internal conversion (IC).