The photochemical R/S isomerization of the title molecule is of interest as it transforms chiral isomers. The reaction is believed to involve a S-1/S-0 conical intersection (CI) similar to the well-known H-atom migration one found for ethylene. Here, we report a new, different CI; subsequent to crossing this CI, the molecule is expected to form primarily the enantiomeric isomer in solution, whereas in the absence of collisions it is likely to dissociate into a vinylidene biradical and a vibrationally and rotationally excited HF. The low energy of this CI suggests it as a major deactivation pathway after electronic excitation. (c) 2007 Elsevier B.V. All rights reserved.