Ab initio spectroscopy and thermochemistry of the BN molecule

Abstract

The lowest1Σ+ and3Π states of the BN molecule have been studied using the quadratic configuration interaction method and (spdf) basis sets. The lowest1Σ+ and3Π states lie extremely closely (Te≈100 cm−1) together; it is not clear which is the ground state. The very small separation should form a useful benchmark for basis sets and electron correlation methods. The dissociation energyD0 is computed to be 103.9±2 kcal/mol. A self-consistent set of spectroscopic constants is derived from a combination of ab initio and experimental data. JANAF-style thermodynamic functions in the range 100–6000 K, including anharmonic, rovibrational coupling, centrifugal stretching, and spin-orbit coupling effects are computed using direct numerical summation over the 25 lowest electronic states. A modified procedure for the latter is outlined that reduces computer time by one or two orders of magnitude without compromise in accuracy.