Electronic to vibrational energy transfer between Rb(5(2)P(J)) and H-2

We have investigated the electronic-to-vibrational (E-V) energy transfer between electronically excited rubidium atoms (Rb 5(2)P(1/2),(3/2)) and hydrogen molecules (H-2). We Have used the CARS (Coherent Anti-Stokes Raman Scattering) spectral technique to probe the internal state distribution of collisionally-populated H-2 molecules. Both scanned CARS spectra and activated CARS spectra reveal that during E-V energy transfer processes H-2 molecules are produced only at the v=1 and v=2 vibrational levels. From scanned and activated CARS spectral peaks two possible population ratios (n(1)/n(2)) are obtained, Through shape simulations of the time-resolved CARS profiles under a simple kinetic model, the actual population ratio nl in, is unambiguously determined to be of 0.59 (o=0.05). This n(1)/n(2) ratio indicates that the H-2 molecules produced by the E-V energy transfer process are 37% populated at the v=1 vibrational level and 63% at v=2, and that the efficiency of the E-V energy transfer is 0.489 for the Rb 5(2)P(1/2)-H-2 system and 0.481 for the 5(2)P(3/2)-H-2 system, coincident with the highest E-V transfer fraction 0.489 under the impulsive model and a collinear collision geometry. (C) 1997 American Institute of Physics.