Knowledge Bank

The hyperfine structures of various lines in the band of the $A¯2\Pi u-X¯2\Pi g$ system of $\mathrm{<mrow\; data-mjx-texclass="ORD">11</mrow>}BO2$, near 5450 {\AA}, have been recorded at very high resolution using molecular beam laser techniques. The results supplement the earlier R-branch measurements of Curl $etal1$, which were taken using intermodulated fluorescence. In particular they show previously-unsuspected perturbations in the upper state hyperfine patterns at many of the places where the rotational lines have recently been found to be slightly $shifted2$. Ground state parameters have been extracted from the combination differences, but no simple model can be devised to fit the upper state, which turns out to be randomly perturbed as a result of extensive vibronic coupling with high vibrational levels of the ground state.