Extended ab initio studies of the vinylidene–acetylene rearrangement

Abstract

The ground state vinylidene-acetylene isomerization was investigated by ab initio molecular electronic structure theory. The coupled-cluster method with single, double, and noniterative inclusion of triple excitations ͓CCSD͑T͔͒; with single, double, and noniterative inclusion of triple and quadruple excitations ͓CCSD͑TQ͔͒; and with full single, double, and triple excitations ͑CCSDT͒ were used to treat the effect of electron correlation. Several correlation-consistent polarized valence basis sets, cc-pVXZ, were employed. Theoretical limiting values of the energetics of the reaction were then deduced from the series of computations. With zero-point energy correction, the energy of reaction is Ϫ42.95 kcal/mol and the reaction barrier is 1.5 kcal/mol. Both agree excellently with experimental values.

On the Origin of Cometary C2and C3: Hydrogen Atom Migration in Diacetylene?

“…Experimental and theoretical studies show that the ground-state energy of vinylidene is about 45 kcal mol À1 above the ground-state energy of acetylene. The energy barrier for the vinylidene to acetylene isomerization is about 10 kcal mol À1 (Dykstra & Schaefer 1978;Krishnan et al 1981;Gallo et al 1990;Ervin et al 1989Ervin et al , 1990Petersson et al 1992;Chang et al 1997;Hayes et al 2001). Consequently, the full energy barrier for the migration of a hydrogen atom from À1 to À2 in ground-state acetylene is about 55 kcal mol À1 .…”

Equilibrium Structure and Spectroscopic Constants of Difluorovinylidene: An ab Initio Study

“…The electronic contribution ⌬E e to this energy difference has been estimated recently by density functional calculations to be approximately 32 kcal/mol (4), i.e., about 2 kcal/mol higher than our best result (⌬E e ϭ 29.7 kcal/mol; see Table 1). We note that the zero-point corrected energy difference between F 2 CC and FCCF is about 14 kcal/mol smaller than the corresponding difference between H 2 CC and HCCH (1,34,35).…”

Spectral patterns and ultrafast dynamics in planar acetylene

“…Lastly, a better understanding of the stretch-bend problem, even in a simplified planar model, is of pressing interest, because of the possible involvement of the stretches in the acetylene-vinylidene isomerization process. The isomerization has been a focus of interest of the pure-bends spectral analysis [13], yet there is reason to think from ab initio calculations [14] that the transition state in the isomerization may involve the stretches as well as the bends. a e-mail: Kellman@Oregon.Uoregon.Edu…”