Abstract Two hitherto unknown difluoromethylselanes, HCF 2 SeH and ClCF 2 SeH, were formed by photolysis of difluoroselenoacetic and chlorodifluoroselenoacetic acids isolated in solid argon. The progress of the photolysis was monitored by FTIR spectroscopy. The photoproducts were identified by comparison of experimental with theoretically predicted spectra and reported spectra for known species. The photochemical decomposition mechanisms of HCF 2 C(O)SeH and ClCF 2 C(O)SeH is presented.