Multireference (single) and double-excitation – configuration interaction (MRD-CI) study of the radicals CN, SiN, and SiP, and the linear structures of HSiP and SiPH in their electronic ground and various excited states

The relative stability of the three low-lying doublet states of the isovalent series CN, SiN, and SiP are calculated with highly correlated MRD-CI wavefunctions. The low-lying 4Σ+, 4Δ, 4Σ−, and 4Π states are analyzed and their equilibrium geometries and Tc values reported. The 4Π state of the radical CN is placed at an excitation energy that agrees with experimental inferences. In SiN, the theoretical treatment predicts a very small Tc value for A2Πi and finds no K2Σ state (earlier assumed), in accordance with recent experiments. The SiP radical contrasts with the other radicals because it possesses a X2Πi ground state and an energetically close-lying A2Σ+ state, in analogy with the experimental situation observed for the isovalent [Formula: see text] radical. The HSiP–SiPH species (linear geometry assumed) are reported for the first time. The energy difference is found to be practically zero in the present treatment. The dissociation energies and the vertical ionization potentials of the linear conformations also have been calculated. The theoretical dipole moments obtained for various electronic states of the AB radicals as well as for the ground states of the HSiP–SiPH components in Cxv symmetry are presented.