Inverted perturbation approach (IPA) potentials and adiabatic corrections of the X 1Σ+ state of the lithium hydrides near the dissociation limits

Laser-induced fluorescence (LIF) spectra of the A–X system of the LiH isotopes, excited by the UV lines of an argon and a krypton ion laser, were observed and analyzed. Three long LIF series of different LiH isotopes were taken with a 3.4 m high resolution spectrograph. The results were combined with previous experimental data to study the breakdown of the Born–Oppenheimer approximation in the X 1Σ+ electronic ground state of the isotopic LiH molecules. Using a quantum mechanical variational method, potential energy curves of the four LiH isotopes were extended almost up to the dissociation limits.