An optical-optical double resonance experiment in LiH molecules: lifetime measurements in the C state

An optical-optical double resonance sub-Doppler experiment is used to measure short nonradiative lifetimes in the C (1)Sigma(+) state of LiH. These lifetimes are expected to result from the strong electronic interaction between the C (1)Sigma(+) state and the continuum of the A (1)Sigma(+) state and to vary with the vibrational quantum number, from nanoseconds to milliseconds. The experimental setup combines a molecular beam of LiH, a first cw laser beam locked to a given A-X absorption line, and a second cw laser beam scanned over C-A absorption profiles. Analysis of these absorption profiles in terms of Voigt profiles shows that their Lorentzian components significantly vary with the vibrational quantum numbers of the C state. Nonradiative decay rates deduced this way are systematically larger than the calculated ones but their variations are similar. Coherent saturation effects cannot be invoked to explain this discrepancy.