Measurement of the vibrational state dependence of the LiH A 1Σ+ dipole moment

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Abstract
Zero field molecular level crossing spectroscopy in the J′=2 rotational state has been employed to measure the electric dipole moment μv of several vibrational levels v′ of the LiH A 1Σ+ excited electronic state. The dipole moments are determined to be μ1=1.88±0.19 D, μ2=1.49±0.18 D, and μ5=0.29±0.05 D, where the quoted uncertainties represent 95% confidence intervals. These experimental values are found to agree rather well with vibrationally averaged dipole moments from the ab initio calculation by Docken and Hinze [J. Chem. Phys. 57, 4928, 4936 (1972)]. The extreme dependence of μv on vibrational level is striking and, on the basis of the ab initio results, can be ascribed to a change in the electronic structure of the LiH A state with internuclear separation.