The methane dication revisited

Abstract

All-electron, ab initio molecular orbital calculations have been performed on electronic states of CH₄²⁺ using perturbative configuration interaction procedures and large sets of Gaussian basis functions with a view to attempting reconciliation between contemporary quantum-chemical information and different sets of experimen-tal data from charge-stripping, threshold photoionization, and double-charge-transfer mass spectrometry. Metastable electronic states of CH₄²⁺ are predicted for D_4h and D_2d symmetries, with charge-stripping experiments likely to populate spin singles of the former symmetry. Investigation of the dissociation of CH₄²⁺ (D_4h) to CH₃⁺ (D_3h)+ H⁺ along the C_2v symmetry pathway indicates that theoretical and experimental data on metastable states of this dication are in accord only if non-Frank-Condon transitions are postulated.