Rovibronic Levels for the (1–3)3Πg Manifold of B2: Exterior Complex Scaling Finite Element Calculations Based on an Adiabatic and a Strictly Diabatic Basis

Abstract

A one-dimensional complex scaled finite element method was applied on an adiabatic basis of B2 in order to find rovibronic term energy values for the (1)3Πg; (v, N)=(0–8, 0–25) and (2)3Πg; (v, N)=(0–10, 0–25) levels. The method was also applied to the (1)3Πg; (v, N)=(0–8, 0–25) and (2)3Πg; (v, N)=(0–1, 0–25) levels in a strictly diabatic framework. Adiabatic single-channel and diabatic coupled-channel total wavefunctions were obtained and used in order to identify the vibrational levels. Comparing levels for the interacting two-state (1–2)3Πg and three-state (1–3)3Πg system, a constant energy shift of about 1.7 cm−1 is found. Comparisons between the adiabatic Born–Oppenheimer (BO) and the diabatic (1)3Πg; (v, N)=(0–8, 0–25) levels show differences between −20 and 7 cm−1, while the corresponding shifts for the (2)3Πg; (v, N)=(0, 0–25) and (1, 0–25) levels are about 50 and 60 cm−1, respectively. A comparison between our three-state approximation and experimental observations of the (2)3Πg–A3Πu electronic transition shows a difference in the line positions of about 665 cm−1. The calculated widths for all but the (1)3Πg; (v, N)=(7–8, 0–25), as well as the (2)3Πg; (v, N)=(0, 0–25) BO and diabatic rovibronic levels, have small but with N increasing predissociation rates. The (1)3Πg; (v>8, N=0–25) BO and the (2)3Πg; (v, N)=(1, 0–25) diabatic levels are strongly predissociated with widths ≥16 cm−1.