Configuration interaction calculations on the propane radical cation, C3H 8 +

Abstract

Proton isotropic hyperfine coupling constants have been calculated for three low-energy nuclear conformations on the ground state potential surface of the propane cation, using a multireference singles and doubles configuration interaction (MR-SDCI) wave function. The lowest point found on the potential surface hadC 2v symmetry and the electronic wave function at this point had2B2 symmetry. At this point, the largest isotropic coupling constant is calculated to be 88.6 G, which is in fair agreement with the experimental value of 98 G obtained in an SF6 matrix at 4 K. No support is found for a “long-bond” ground state of lower symmetry thanC 2v . AnotherC 2v minimum on the ground state potential energy surface was found at which the wave function had2 B 1 symmetry. At this point, two large coupling constants of 198 G and 35 G were calculated. AC 2v stationary point was also found on the ground state potential surface at which the wave function had2 A 1 symmetry. At this point, couplings of 86 G and 25 G were obtained. None of these agree closely with the other experimental result of couplings at both 100–110 G and 50–52.5 G which was obtained in freon matrices. It is suggested that the latter spectra might correspond to a dynamical average of two distorted2 A' states inC s symmetry.