[Temperature dependence of cross sections for energy transfer processes of Rb(7S-5D)-H2, He]

Rb vapor, mixed with H2 or He, was irradiated in a glass fluorescence cell with pulses of radiation from a YAG-laser-pumped OPO laser, populating 5D or 7S state by two-photon absorption. The temperature dependence of the cross sections for 5D-7S transfer induced by collisions with He atoms and H2 molecules was determined using methods of atomic fluorescence. The resulting fluorescence included a direct component emitted in the decay of the optically excited state and a sensitized component arising from the collisionally populated state. At the different densities, the authors have measured the relative time-integrated intensities of the components and fitted a three-state rate equation model to obtain the reactive and nonreactive cross sections for Rb(7S-5D)-H2, He collisions. The cross sections of transfer for Rb(7S)+H2-->Rb(5D)+H2 decrease with increasing T. The cross sections for 5D-->7S increase with increasing T. At the different temperatures, the cross sections of transfer for (7S-5D)-He collisions coincide with the principle of detailed balance. The total transfer rate coefficients out of the 7S or 5D state for He were small. The total quenching rate coefficient out of the 7S or 5D state was much larger for H2. In the case of H2, the quenching rate coefficient corresponds to reaction and nonreactive energy transfer. In reaction of Rb(7S, 5D)+H2-->RbH+H, the ratio between the reactive cross sections was found to be sigma(-)[Rb(7S)+H2]/sigma(-)(Rb(5D)+H2]=1.5. The relative reactivity with H2 was in an order of Rb(7S)>Rb(5D).