Rotational analysis and deperturbation of the C2Σ+–X2Σ+ band systems of BeH and BeD

Abstract

A new C2Σ+–X2Σ+ transition of BeH and BeD is observed in a beryllium are in hydrogen or deuterium gas mixed with argon. The rotational analysis of the most intense of these strongly red degraded bands, which involve ν′ = 0–2 for BeH and ν′ = 0 for BeD, allows one to derive molecular constants for the new C2Σ+ state. The latter has a large internuclear equilibrium distance (re = 2.301 Å) and a shallow potential energy minimum [Formula: see text]. The principal molecular constants determined are:C2Σ+Tc = 30 953.94 cm−1[Formula: see text]Rotational perturbations between the C2Σ+ and A2Π states are observed in the C–X bands of BeH and BeD and in two new A–X bands of BeH (4–4 and 5–5) which have also been observed and analyzed. These perturbations are treated by a matrix approach and yield a value for the interaction matrix element [Formula: see text].The C–X bands analyzed involve the higher vibrational levels of the X2Σ+ state and allow, therefore, a substantial improvement of the ground state molecular constants to be made and a good Rydberg–Klein–Rees (RKR) potential energy curve to be calculated. The limiting curve of the predissociation confirms the previous value of the dissociation energy [Formula: see text] and indicates that a small maximum, less than 200 cm−1, could exist at [Formula: see text] in the ground state potential energy curve.Franck–Condon factors for the C2Σ+–X2Σ+ bands of BeH and BeD are also calculated.