Hyperfine Structure of theB Σ2→X Σ2Transition of the LaO Molecule

The O-O band of the $B {}_{}{}^2{}_{}{}^{}\Sigma \to X {}_{}{}^2{}_{}{}^{}\Sigma$ transition of lanthanum oxide has been studied using an interference spectrometer HYPEAC and a "dressed-walls" hollow cathode. The accuracy of the measurements allows a detailed study of nuclear hyperfine effects. A theoretical interpretation of experimental results is proposed which takes into account residual fine- and hyperfine-interaction contributions. A satisfactory explanation of the variation with $N$ of the intensities is obtained when introducing intermediate coupling $b_{{\beta }_S}-b_{{\beta }_J}$ effects in the ground state. From the comparison between experimental and theoretical results, the following values of some hyperfine- and fine-structure parameters are deduced, i.e., for the $X {}_{}{}^2{}_{}{}^{}\Sigma$ state ${\gamma }_{SR}=2.57\mathrm{}\pm 0.25$ mK and $b=123.5\mathrm{}\pm 1.8$ mK, and for the $B {}_{}{}^2{}_{}{}^{}\Sigma$ state $b^{\prime }=21.7\mathrm{}\pm 2.0$ mK and $c^{\prime }=-5\pm 12$ mK.