Equilibrium geometries and hyperfine interactions in propane and cyclopropane cations

Abstract

The equilibrium geometries of the propane cation in its three lowest electronic states, 2B1, 2B2 and 2A1(C2v symmetry assumed), have been calculated by the UHF method within the ab initio MO-LCAO-SCF approximation. The 2B1 state is predicted to be lowest in energy and the 2B2 and 2A1 states to be of almost the same energy, 12 kcal mol–1 above the 2B1 state. The isotropic hyperfine coupling constants have been calculated and compared with experimental data. The calculations confirm the e.s.r. identification of the 2B1 state, obtained in an SF6 matrix. The previous experimental assignment, 2B2, for the state obtained in Freon matrices was found to be ambiguous and an assignment to the 2A1 state can not be ruled out. Dipolar hyperfine coupling constants have been calculated for the 2B1, 2B2 and 2A1 states of the propane cation and for the 2A1 ground state of the cyclopropane cation. In the latter case, comparison with experimental data has been made with reasonable agreement. The equilibrium geometry agrees well with previous calculations. Complementary experimental data for the propane and cyclopropane cations are reported.