Structures and energies of the two lowest-lying electronic states in the sulphido-borons radical cations, RBS^+· (R = H, F, Cl and CH₃)

Abstract

A theoretical characterization has been performed for the structures and energies of four sulphido-borons radical cations, RBS^+· (R = H, F, Cl and CH₃) in their lowest-lying π and Σ and related electronic states. Data for the neutral species are also included. Geometries, rotational and vibrational frequencies are determined at the UHF/6–31G(d) level. Adiabatic ionization energies (IE _a) and excitation energies are obtained at the fourth-order Møller-Plesset perturbation theory using the 6–31 G(d, p) basis set. For the HBS/HBS^+· system, calculations with different basis sets and configuration interaction are also carried out for purposes of comparison. In general, calculated and experimental structural parameters are in good accord supporting the assignments previously made. Due to the inherent difficulty of computational methods, calculated IE _as are systematically underestimated with errors of 0·3 eV being typical. The excitation energies ΔE(²Σ ← ²Π) in the radical cations are however well predicted with errors of ∼0·1eV. The Jahn-Teller effect in the ground state of CH₃BS^+· is studied in details.