Laser fluorescence excitation spectroscopy of BNe electronic states correlating with the excited valence B(2s2p2 2D) atomic asymptote

Abstract

The laser fluorescence excitation spectrum of the BNe van der Waals complex, in the vicinity of the B atom 2s2p2 2D←2s22p 2P transition at 208.9 nm, is reported. A total of six partially resolved molecular bands, as well as a broad, unstructured feature to the blue of these bands, have been observed. Three BNe electronic states, denoted as C 2Δ, D 2Π, and E 2Σ+, correlate with the B(2s2p2 2D)+Ne atomic asymptote, and the observed bands are assigned as (v′,0) progressions of the C 2Δ−X 2Π1/2 and D 2Π–X 2Π1/2 band systems. Rotational analysis of the C–X bands has been carried out, and spectroscopic constants characterizing the upper and lower states determined. The onset of the continuous excitation is assigned as the energy to reach the B(2s2p2 2D)+Ne atomic asymptote. Identification of this threshold has allowed the determination of dissociation energies of the X, C, and D states. The observation of banded features in this wavelength range contrasts sharply with the continuous free←bound excitation in the B 2Σ+–X 2Π1/2 transition, because of the purely repulsive B(2s23s 2S)–Ne interaction [X. Yang, E. Hwang, P. J. Dagdigian, M. Yang, and M. H. Alexander, J. Chem. Phys. 103, 2779 (1995)]. The differences in the binding energies of the BNe electronic states are discussed in terms of their expected electronic structures.