Binding enthalpies for alkali cation-benzene complexes revisited

The geometries and binding enthalpies of M+(benzene) complexes (M = Li, Na, K, Rb, and Cs) were obtained from large basis set second-order perturbatio n theory and coupled cluster theory calculations. The best DeltaH(298) esti mates (in kcal/mol) are Li+(benzene) = -36.8 +/- 0.2 (theory) vs -37.9 and -39.3 +/- 3.2 (expt), Na+(benzene) = -24.7 +/- 0.3 (theory) vs -28.0 +/- 1. 5 and -22.5 +/- 1.5 (expt), K+(benzene) = -20.1 +/- 0.4 (theory) vs -19.2 a nd -17.1 +/- 0.9 (expt), Rb+(benzene) = -16.4 +/- 0.2 (theory) vs -16.4 +/- 0.9 (expt), and Cs+(benzene) = -12.5 +/- 0.2 (theory) vs -15.1 +/- 1.1 (ex pt). The present findings include small corrections for core/valence correl ation effects and lead to binding enthalpies uniformly larger than those of previous theoretical studies.