THE MCH(2)(- DO SCCH2+ AND TICH2+ HAVE C-S OR C-2V SYMMETRY AND A COMPARISON OF THE B3LYP METHOD TO OTHER APPROACHES() SYSTEMS )

ScCH2+ and TiCH2+ are found to have C-s symmetry, while the remaining systems have the expected C-2v symmetry. The C-s symmetry structure is favored for ScCH: and TiCH: because it allows donation from one of th e CH bonds into an empty metal 3d orbital. This distortion stabilizes the systems by less than 2 kcal/mol. For V through Cu there are no emp ty 3d orbitals of the correct symmetry, and therefore the distortion t o C-s is unfavorable. The corrected B3LYP binding energies are in good agreement with experiment and our previous best estimates.