The X2Σ+, (2)2Σ+, and (2)2Π States of BaLi

Abstract

Fourier transform spectrometry of the thermal emission at 1100°C of Ba6Li and Ba7Li has been performed in the infrared spectral region from 4000 to 8400 cm−1. A total of 7075 lines are ascribed to several bands, 11 for Ba6Li, 8 for Ba7Li, of the (2)2Σ+→X2Σ+ and (2)2Π→X2Σ+ systems. A consistent set of molecular constants describing the v = 0, 1, 2 levels in X2Σ+ and (2)2Σ+, and v = 0, 1 in (2)2Π is obtained from the simultaneous adjustment of all the data corresponding to v-connected bands for each isotopic species. Information is also obtained for X2Σ+(v = 3) and (2)2Π(v = 2) from an independant treatment of the (2-3) band in (2)2Π→X2Σ+. The standard deviation of the different fits appears to be close to the experimental accuracy, 0.004 cm−1. Effective molecular constants at equilibrium are derived for the three states. The interpretation of the evolution of different effective interactions with vibration and rotation, particularly the spin-orbit interaction in the (2)2Π state, leads us to invoke the presence of one or more perturbing states. Also, the relative intensities between branches within the (2)2Σ+→X2Σ+ and (2)2Π1/2→X2Σ+ bands which do not correspond to those expected for pure transitions are explained in terms of interference between parallel and perpendicular transition moments. Values of μ|| and μ⊥ can be evaluated for the (0-0) transitions.