Theoretical spectroscopy and metastability of BeS and its cation

Abstract

Multiconfiguration self-consistent field and multiconfiguration reference interaction including the Davidson’s correction techniques were employed to calculate the potential energy curves (PECs) of the BeS/BeS + electronic states correlating to the 4/5 lowest dissociation limits. After nuclear motion treatment, we deduced reliable spectroscopic data for the neutral and cationic bound states. For BeS, the transition moments and spin-orbit couplings were also evaluated and used later with the PECs to deduce the rovibronic transition probabilities and the radiative lifetimes in the low-lying states, and to investigate the unimolecular decomposition processes of BeS (X 1Σ +, A 1Π, 3Σ + and B 1Σ +) leading to Be( 1S g) + S( 3P g). The prominent mechanism is a spin-orbit induced predissociation via the repulsive BeS(1 3Σ −) state. Finally, we give the single ionization spectrum of BeS (X 1Σ +) populating the BeS + (X 2Π, 1 2Σ −, 1 2Σ +, 1 2Δ, 2 2Σ +, 2 2Π and 3 2Π) electronic states. The adiabatic ionisation energy of BeS is estimated to be ∼9.15 eV.