Teratomic recombination in alkali metal–noble gas vapors

The teratomic recombination rates for the reaction M*+2X→MX* (A 2Π)+X have been studied for Rb–Xe, Na–Ar, Kr, Xe, and Li–Ar, Kr, Xe. This analysis employs data and molecular potential determinations from earlier measurements where free alkali M was optically excited to M* in the presence of noble gas X and the MX* (A 2Π) →MX(X 2Σ) fluorescence resulting from teratomic recombination was measured. Collisional processes compete with radiative decay, so that in the low [X] limit where dissociation collisions are negligible the ratio of bound molecular to atomic photon emission gives the branching ratio between the molecular formation rate and the known atomic radiative rate. The molecular spectrum is observed as a continuum whose intensity profile may be used to infer a bound state vibrational distribution at each [X]. Both bound and quasibound states are included in this distribution, as both contribute to the observed molecular spectra. The low pressure limit of this distribution yields the teratomic recombination rate as a function of binding energy, and the total recombination rate constant kf. It is generally found that this distribution per quantum state is almost independent of binding energy; i.e., the probability of molecular formation appears to be about the same for all bound states, it does not favor the highest bound levels. When the density of states is considered, weakly bound molecules are formed more frequently, but this weighting depends on the shape of the potential rather than the gas temperature. Comparison with theoretical models is made, and reasons for the discrepancies are discussed.