Ab initio molecular orbital calculations were performed on species associated with the bimolecular reaction of protonated methylamine (CH3NH3+) with methylcalcium (CaCH3) to form the valence-Rydberg bonded complex H3CH3N.+CaCH3. Gradient geometry optimizations and frequency calculations were performed at levels of theory up to and including UMP2(full)/6-311 G(d,p) augmented by diffuse functions on the nitrogen atom. The complex H3CH3N.+CaCH3 is bound by 9.77 kcal mol(-1) relative to reactants at the projected second-order Moller-Plesset perturbation theory (PMP2) level, and both the charge and unpaired spin densities are delocalized between calcium and the adjacent amino group, the region of the valence-Rydberg bond. A rearranged product. [H3CH2N:-->CaH ... CH3](+.), lies 12.38 kcal mol(-1) below the valence-Rydberg complex, and is bound by 9.66 kcal mol(-1) relative to dissociation products [H3CH2N:-->CaH](+) + . CH3. The rearranged species is a distonic ion, with the positive charge mainly on calcium, and the unpaired electron on the carbon atom of the quasi-planar CH3 moiety. A transition structure interconverting the two isomers lies ca. 21 kcal mol(-1) above the higher-energy isomer, but is far above the dissociation limits of either species. Thus, in the gas phase at thermal energies, the valence-Rydberg complex and the lower-energy isomer [H3CH2N:-->CaH . .. CH3](+.) will not interconvert through this transition state.