Summary: 6852 J. Am. Chem. SOC.1982, 104, 6852-6854
31G**) for all data and used these throughout the text (see Table
I). All species reported are considered to be equilibrium
structures, since the force-constant matrix obtained from the
6-31G* (CH62+)and 3-21GS (C2Hd2+, C2H6'+$ and C2Hs2+)
optimized geometrias have no negative eigenvalues,except 2, which
has one. The zero-point vibrational energies deduced from these
force constants (see Table I) are after scalings included as our
final adjustment in all subsequent reaction energies given at the
MP3/6-31G1* level (Scheme I).
The methane dication, CH42+,is trivalent and tetracoordinate
with a planar (D4*symmetry) geometry? Interaction of molecular
hydrogen with the empty pz orbital of CH42+results in CH62+.
Diprotonated methane is hexacoordinate. The minimum-energy
equilibrium structure 1 (Chart I) calculated for CH?+ (see Table
I) has two orthogonal 3c-2e interactions (C2"symmetry), em-
phasizing the importance of this effect. The structure 2 with only
one such interaction may be regarded as the transition for transfer
of one 3c-2e interaction in 1and is 2.6 kcal/mol higher in energy.
The stabilization of 1 gained with respect to CH42+amounts to