Electronic to vibrational energy transfer between Rb(5 2PJ) and H2

Abstract

We have investigated the electronic-to-vibrational (E-V) energy transfer between electronically excited rubidium atoms (Rb 5 2P1/2,3/2) and hydrogen molecules (H2). We have used the CARS (Coherent Anti-Stokes Raman Scattering) spectral technique to probe the internal state distribution of collisionally-populated H2 molecules. Both scanned CARS spectra and activated CARS spectra reveal that during E-V energy transfer processes H2 molecules are produced only at the v=1 and v=2 vibrational levels. From scanned and activated CARS spectral peaks two possible population ratios (n1/n2) are obtained. Through shape simulations of the time-resolved CARS profiles under a simple kinetic model, the actual population ratio n1/n2 is unambiguously determined to be of 0.59 (σ=0.05). This n1/n2 ratio indicates that the H2 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 2P1/2−H2 system and 0.481 for the 5 2P3/2−H2 system, coincident with the highest E-V transfer fraction 0.489 under the impulsive model and a collinear collision geometry.