Collision Energy Transfer Of Excited Rb₂,Na₂ By H₂

Coherent anti-Stokes Raman spectroscopy(CARS) has been used to investigatethe electronic-to-rovibrational levels energy transfer between electronically excitedRb2 and H₂, and then analyze the internal state distribution of H₂ after energy transferwith Na2(A¹Î£_u⁺).(1) In this CARS experiment, the S—branch(â–³v =1,â–³J=2) transition of H₂ areexcited by two laser pulses, the pump and the Stokes, respectively, centered at 532and 690 nm. The internal state distribution of collisionally populated H₂ has probed.The scanned CARS spectra reveal that during energy transfer processes H₂ moleculesare produced only at the V=1, J=1,2 and V=2, J=0,1,2 rovibrational levels. Fromscanned CARS spectral peaks the population ratios are obtained. The n₁/n₅,n₂/n₅,n₃/n₅and n4/n 5 are 3.57±0.71,2.65±0.53,3.00±0.60å’Œ0.93±0.17,respectively, where n1,n₂,n₃,n₄ and n₅ represent the number densities of H₂ at the rovibrational levels(2,0),(2,1),(2,2),(1,1)and(1,2), respectively. The population ratios indicate that theH₂ molecules produced by the energy transfer process are 83% populated at the V=2vibrational level and 17% at V=1.The relative fractions (＜fV＞:＜fR＞:＜fT＞) ofaverage energy disposal are derived as (0.48, 0.01, 0.51), having major translationaland vibrational energy release. Through semilog plot of the time—resolved CARSprofiles under a simple kinetic model at the experimental conditions of T=573K andP=5×103Pa,collisional transfer rate coefficients k₁₂=(3.1±0.6)×10^-14cm^-3s^-1 and k₂=(4.9±1.0)×10^-15cm^-3s^-1 have been obtained.(2) The scanned CARS spectra reveal that during energy transfer processes H₂molecules are produced at the V=1, 2and 3 vibrational levels. From scanned CARSspectral peaks two possible populations ratios (n₁/n₂) are obtained. Through shapesimulations of the time resolved CARS profiles under a kinetic model, the actualpopulation ratio n1/n2 is determined to be of 1.82. This n₁/n₂ ratio indicates that the H₂molecules produced by the energy transfer process are 0.55 populated at the V=1 level, 0.29 at V=2 and 0.16 at V=3. The relative fraction (＜fV＞:＜fR＞:＜fT＞) of averageenergy disposal are derived as (0.46, 0.03, 0.51), having major vibrational andtranslational energy release. This consequence supports a collinear collision geometryin ratio Na2-H2 energy transfer.