Li + affinity of C 2H 3 and C 2H 5 radicals. Ab initio characterization of Li +-radical complexes

Abstract

Ab initio molecular orbital calculations at the UHF-MP2/6-31G ∗∗ level of theory have been carried out on neutral C 2H 3 and C 2H 5 radicals and their Li + ion adducts, in order to determine the binding energies (Li + affinity) for C 2H 3Li + and C2H 5Li +. Calculations include diffuse functions, and corrections for electron correlation and zero-point vibrational energies (ZPEs). Our predictions for the binding energies of Li + to C 2H 3 and C 2H 5 are 21.4 and 17.8 kcal mol −1 respectively, which are not very different from those between Li + and closed-shell homologous molecules. In the case of the C 2H 3 and Li + system, inclusion of diffuse functions with the 6-311G ∗∗ basis sets leads to a decrease in the binding energy by 0.7 kcal mol −1, while the ZPE corrections with the 6-31G ∗∗ basis sets also lead to a decrease by 0.8 kcal mol −1. The coulombic character of the Li + ion, rather than the favorable electron delocalization in the adduct products, is the determining factor for relative stabilities. The overall results support the interpretation of our recent experimental measurements of Li + ion attachment to hydrocarbon radicals.