“…In the case of BO, there are two extensive band systems, the A 2 P-X 2 R and B 2 R-X 2 R, which have been studied since the early days of quantum mechanics, for example, by Mulliken [1]. Most relevant to the present work are the recent analyses of these band systems by Coxon et al [2] and M elen et al [3]. In addition, the microwave spectra of the two lowest rotational transitions of the radical have been reported by Tanimoto et al [4].…”