Radiative lifetimes, quenching cross sections and population mechanisms of the C1Πu, 23Πg and 1 3Δg states of 7Li2

The laser- and collision-induced fluorescence of Li2 molecules in a heat-pipe, excited by a tunable frequency-doubled mode-locked cavity-dumped cw dye laser into selected rovibrational levels of the C1Πu state, was observed with spectral resolution using a monochromator and with temporal resolution using the single-photon counting technique. The effective lifetimes of the directly excited C1Πu state and of the collisionally excited 23Πg and 1 3Δg states were measured as a function of the lithium vapor pressure and the argon buffer gas pressure. This yields the radiative lifetimes and collisional quenching cross sections of the three states. It is shown that the population mechanism of the 23Πg and 1 3Δg states is the collisional energy transfer from the C1Πu state. Measurement of the total fluorescence intensities emitted from the excited states under cw laser excitation provides the cross sections for the collisoinal population transfer.