Substitution effects on the properties of unsaturated carbenes: fluorovinylidene (HFC:C:)

Abstract

Ab initio molecular electronic structure theory has been used to study the fluorovinylidene-fluoroacetylene isomerization reaction on the C[sub 2]HF singlet ground-state potential energy surface. The [tilde X] [sup 2]A[prime] ground state of the fluorovinylidene anion and the two lowest triplet states ([sup 3]A[prime] and [sup 3]A[double prime]) 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 [tilde X] [sup 1]A[prime] fluorovinylidene is predicted to be 2.4 kcal mol[sup [minus]1]. After correction for zero-point vibrational energies, an activation energy of [approximately]0.8 kcal mol[sup [minus]1] is obtained. The [Delta]E for isomerization to fluoroacetylene is [approximately]44 kcal mol[sup [minus]1]. The adiabatic electron affinity of ground-state fluorovinyldene is predicted to be 1.62 eV. The [sup 3]A[prime] and [sup 3]A[double prime] states of neutral fluorovinylidene are predicted to lie very close together in energy ([Delta]T[sub 0] = 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, the authors' best results indicate that the [sup 3]A[prime] state may be the lowest triplet state for fluorovinylidene (T[sub 0]more » = 1.30 eV). 53 refs., 1 fig., 11 tabs.« less