SUBSTITUTION EFFECTS ON THE PROPERTIES OF UNSATURATED CARBENES - FLUOROVINYLIDENE (HFC=C-)

Ab initio molecular electronic structure theory has been used to study the fluorovinylidene-fluoroacetylene isomerization reaction on the C2HF singlet ground-state potential energy surface. The X 2A' ground state of the fluorovinylidene anion and the two lowest triplet states (3A' and 3A'') of neutral fluorovinylidene have also been investigated. The effects of electron correlation were included via configuration interaction and coupled-cluster methods. The classical barrier for 1,2-hydrogen migration in X 1A' fluorovinylidene is predicted to be 2.4 kcal mol-1. After correction for zero-point vibrational energies, an activation energy of approximately 0.8 kcal mol-1 is obtained. The DELTAE for isomerization to fluoroacetylene is approximately 44 kcal mol-1. The adiabatic electron affinity of ground-state fluorovinylidene is predicted to be 1.62 eV. The 3A' and 3A'' states of neutral fluorovinylidene are predicted to lie very close together in energy (DELTAT0 = 0.12 eV). In general, the theoretical results reported here are in excellent agreement with negative ion photodetachment spectroscopy results reported in the preceding paper by Gilles, Lineberger, and Ervin. However, our best results indicate that the 3A' state may be the lowest triplet state for fluorovinylidene (T0 = 1.30 eV).