Vibration-Vibration Energy Transfer Between Highly Vibrational Excited RbH and H2, N2

Rb-H-2 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(X (1)Sigma(+), v ''=0 similar to 2) generated in the reaction of Rb(6D) with H-2. Vibrational-state-specific total-removal relaxation rate coefficients, k(v)(M), for RbH(X, (1)Sigma(+), v ''=15 similar to 22) by M=H-2 and N-2 were investigated in a pump and probe configuration. By the overtone pumping with a cw diode laser, highly vibrational states v ''=15 similar to 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 A (1)Sigma(+) (v')-> X-1 Sigma(+()v '') transition was monitored. Based on the Stern-Volmer equation, the total relaxation rate coefficient k(v)(H-2) were yielded. A plot of k(v)(H-2 + N-2) VS a (mole fraction H-2) yields a line with a slope of k(v)(H-2)-k(v)(N-2) and an intercept of k(v) (N-2). The values of k(v) (H-2) obtained from the slope of the fitted lines compare well with determined values of the k(v)(H-2) from the Sern-Volmer plots. At v ''<18, the rate coefficients k(v)(M) increases linearly with vibrational quantum number. This linear region is dominated by single quantum relaxation (Delta v=1) collisional propensity rules. The region (v ''>= 18) where the dependence is much stronger than linear shows significant contribution from multiquantum (Delta v >= 2) relaxation or resonant vibration-vibration energy transfer between highly vibrationally excited RbH and H-2 or N-2. For RbH(v '') + N-2(0), we measured the time-profile of v ''=16 after preparation of v ''=21. A clear bimodal distribution was observed. The first peak is due to resonant vibration-vibration energy transfer: RbH(v ''=21)+ N-2 (0)-> RbH(v ''=16)+N-2 (1). The much broader second peal:, at longer time delays, is due to sequential single-quantum relaxation. Although the second process results in a distributior. 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.