High-spin electronic states of the experimentally observed molecular ions methylenemanganese (MnCH2+) and methylenechromium (CrCH2+)

Abstract

The /sup 7/B/sub 1/ electronic state of MnCH/sub 2//sup +/ and /sup 6/B/sub 1/ state of CrCH/sub 2//sup +/ have been investigated with nonempirical molecular electronic structure theory. Large Gaussian basis sets were used in conjunction with explicity correlated wave functions. Equilibrium geometries were predicted at the self-consistent-field level of theory, yielding for MnCH/sub 2//sup +/ r/sub e/(Mn-C) = 2.076 angstrom, THETA/sub e/(HCH) = 114.5/sup 0/ and for CrCH/sub 2//sup +/ r/sub e/(Cr-C) = 2.064 angstrom, THETA/sub e/(HCH) = 113.5/sup 0/. The M/sup +/-CH/sub 2/ bond dissociation energies for these high-spin electronic states are significantly less than the ground-state bond energies deduced from laboratory measurements by Beauchamp and co-workers. This comparison suggests that the true electronic ground states of MnCH/sub 2//sup +/ and CrCH/sub 2//sup +/ may be the lower spin quintet and quartet states, respectively.