A complete active space self-consistent field and multireference configuration interaction analysis of the SiN B 2Σ+−X 2Σ+ transition moment

The electronic transition dipole moment function, Re(R), for the SiN B 2Σ+ ↔ X 2Σ+ transition has been studied by complete active space self-consistent field calculations followed by the multireference singles plus doubles configuration interaction level of theory. It has been found that Re(R) for 2.00 ⩽ R ⩽ 3.45 a0 is a descending function of R and can be described by a fourth-order polynomial. Using arguments of orbital occupancy and the nature of the molecular orbitals involved in the process, it has been shown that the reported explanation for this behaviour is only partially correct, i.e. the negative dependence of Re(R) on R can be attributed to a strong configuration mixing in the B 2Σ+ state of SiN, but it cannot be explained based on the chemical similarity between silicon and carbon. Consequently, theoretical results for the isovalent CN B 2Σ+ ↔ X 2Σ+ transition cannot be used to explain the behaviour of Re(R).