The previously reported ' A g , A , , and ' B states of ionized e;hane are characterized at several levels of theory. %he diborane-like -A state, which gives rise to the observed ESR spectrum, is predicted by SC5 and CCD calculations not to exist in a separate minimum from the A,, state formed by ionization of the C-C bond. However, as re orted by Lunell and Huang, second-order Moller-Plesset theory places the A lowest, provided polarization functions are included on carbon. QCISD theory predicts that both2 A states correspond to potential energy minima, but places the long-bond A , state lower, at least with moderately large basis sets. F orbitals on carbon statilize the diborane structure more than the long-bond one. When a potential energy surface is generated for a series of fixed C-C bond lengths by optimizing all variables except for the C-C bond length with MP2 theory and calculating the energy with QCISNT), the 'Ag state is predicted to be the lowest energy state with the 'A,, state 1.83 kJ/mol above it. The two A states are predicted to be separated by a barrier 2.79 kJ/mol above the lower state. This barrier is above the zero-point energy in the C-C stretch for the lower state but below the ZPE for this stretch in the upper state, which is therefore predicted not to exist as a stable species. A single quantum of vibrational excitation in the low frequency C-C stretch is predicted to yield an ion with a poorly defined C-C bond length. The highest levels of theory employed give poor agreement with the experimental hyperfine coupling constants. The discrepancy could either be due to neglect of vibrational effects, to poor inherent accuracy of the calculation, as one author has concluded, or to compression of the ion by the matrix as suggested by another. The ' 8 , state is found to be higher in energy than the A states at all theoretical levels and is predicted to have a large (160.2-177.4 G) hyperfine coupling from four hydrogens. The transition state for simultaneous exchange of two hydrogen atoms between the carbons by a diborane structure is predicted to lie above the lowest energy fragmentation threshold, in agreement with experiment.