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(C_2v 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.