CHEMICAL BONDS AND ELECTRONIC STRUCTURES OF THE METHONIUM CATIONS ${\rm CH}_{6}^{2+}$ AND ${\rm CH}_{7}^{3+}$

Six isomers with C-2v, D-3h, C-5v, D-2d, O-h, and C-4v symmetries of CH62+ and two isomers with C-3v and C-2v symmetries of CH73+ are investigated at the high ab initio level combined with the natural bond orbital and the atoms-in-molecules theorems. The hyperconjugative interaction and the electron topological analyses indicate that the multiple three-center two-electron (3c-2e) hyperbond is the common chemical-bonding basis for CH62+ and CH73+ species. In contrast to the planar 3c-2e (triangle structure) and planar four-center four-electron (4c-4e) hyperbonds in CH5+ isomeric species, the 3c-2e hyperbond in CH62+ (C-4v) is linear while the 4c-4e hyperbonds in CH62+ (C-5v, D-2d, O-h) are unplanar. CH62+ (C-2v) and CH73+ (C-3v) as the global minima have many resonance structures predicted by the natural bond resonance theory, indicating the high possibility of the hydrogen scrambling which is similar to the scenario of CH5+.