LI- AB-INITIO CHARACTERIZATION OF LI+-RADICAL COMPLEXES( AFFINITY OF C2H3 AND C2H5 RADICALS )

Ab initio molecular orbital calculations at the UHF-MP2/6-31G(*) leve l of theory have been carried out on neutral C2H3 and C2H5 radicals an d their Lif ion adducts, in order to determine the binding energies (L i+ affinity) for C2H3-Li+ and C2H5-Li+. Calculations include diffuse f unctions, and corrections for electron correlation and zero-point vibr ational energies (ZPEs). Our predictions for the binding energies of L i+ to C2H3 and C2H5 are 21.4 and 17.8 kcal mol(-1) respectively, which are not very different from those between Li+ and closed-shell homolo gous molecules. In the case of the C2H3 and Li+ system, inclusion of d iffuse 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 wit h 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 ele ctron delocalization in the adduct products, is the determining factor for relative stabilities. The overall results support the interpretat ion of our recent experimental measurements of Li+ ion attachment to h ydrocarbon radicals.