Abstract：Rb-H2 mixture was irradiated with pulses of 696.4 nm radiation from a OPO laser, populating 6D state by two-photon absorption. The vibrational levels of RbH(Х 1Σ+,ν″=0～2) generated in the reaction of Rb(6D) with H2. Vibrational-state-specific total-removal relaxation rate coefficients, kν(M), for RbH(Х 1Σ+,ν″=15～22) by M=H2 and N2 were investigated in a pump and probe configuration. By the overtone pumping with a cw diode laser, highly vibrational states ν″=15～22 of RbH in its ground electronic state were obtained. Another diode laser was used to probe the prepared vibrational state. The decay signal of laser induced time-resolved fluorescence from A1Σ+(ν′)→Х1Σ+(ν″) transition was monitored. Based on the Stern-Volmer equation, the total relaxation rate coefficient kν(H2) were yielded. A plot of kν(H2+N2) vsα(mole fraction H2) yields a line with a slope of kν(H2)-kν(N2) and an intercept of kν(N2). The values of kν(H2) obtained from the slope of the fitted lines compare well with determined values of the kν(H2) from the Sern-Volmer plots. At ν″<18, the rate coefficients kν(M) increases linearly with vibrational quantum number. This linear region is dominated by single quantum relaxation (Δν=1) collisional propensity rules. The region (ν″≥18) where the dependence is much stronger than linear shows significant contribution from multiquantum (Δν≥2) relaxation or resonant vibration-vibration energy transfer between highly vibrationally excited RbH and H2 or N2. For RbH(ν″)+N2(0), we measured the time-profile of ν″=16 after preparation of ν″=21. A clear bimodal distribution was observed. The first peak is due to resonant vibration-vibration energy transfer: RbH(ν″=21)+N2(0)→RbH(ν″=16)+N2(1). The much broader second peak, at longer time delays, is due to sequential single-quantum relaxation. Although the second process results in a distribution that is much more spread out in time, the peak height is in the same order of magnitude, indicating that the two processes are at least comparable in probability.
[1] Flynn G W, Parmenter C S, Wodtke A M. J. Phys. Chem., 1996, 100: 12817. [2] Yuan L W, Du J, Mullin A S. J. Chem. Phys., 2008, 129: 014303. [3] Lenzer T, Luther K , Reihs K, et al. J. Chem. Phys., 2000, 112(9): 4090. [4] Miller E M, Murat L, Bennette N, et al. J. Phys. Chem., 2006, A110: 3266. [5] Silva M, Jongma R, Field R W, et al. Annu. Rev. Phys. Chem., 2001, 52: 811. [6] Wu J, Huang R, Gong M, et al. J. Chem. Phys., 1993, 99(9)：6474. [7] Park H, Slanger T G. J. Chem. Phys., 1994, 100(1): 287. [8] Yamasaki K, Fujii H, Watanabe S, et al. Phys. Chem. Chem. Phys., 2006, 8: 1936. [9] Jongma R T, Wodtke A M. J. Chem. Phys., 1999, 111(24): 10957. [10] Watanabe S, Fujii H, Kohguchi H, et al. J. Phys. Chem., 2008, A112: 9290. [11] Fan L H, Chen J J, Liu Y Y, et al. J.Phys.Chem., 1999, A103: 1300. [12] SHEN Xiao-yan, WANG Shu-ying, LIU Jing, et al(沈晓燕，王淑英，刘 静，等). Spectroscopy and Spectral Analysis(光谱学与光谱分析), 2011, 31(1): 39. [13] Gallagher A, Lewis E L. J. Opt. Soc. Am., 1973, 63(7): 864. [14] Stwalley W C, Zemke W T, Yang S C. J. Phys. Chem. Ref. Date., 1991, 20: 153. [15] Yang X M, Kim E H, Wodthe A M. J.Chem.Phys., 1992, 96(7): 5111. [16] Mack J A, Mikulecky K, Wodthe A M. J.Chem.Phys., 1996, 105(10): 4105.
