高激发振动态RbH(Х~1Σ^+,ν″=15～22)与H_2,N_2的振动-振动碰撞能量转移

Vibration-Vibration Energy Transfer Between Highly Vibrational Excited RbH and H_2,N_2

脉冲激光激发Rb原子至6 D态,Rb(6 D)与H2反应生成RbH(Х1Σ+,ν″=0～2)振动态。研究了RbH(Х1Σ+)高位振动态与H2,N2间的碰撞弛豫过程,利用泛频泵浦分别激发Х1Σ+(ν″=0)至Х1Σ+(ν″=15～22)各振动态,检测激光激发Х1Σ+(ν″)至A1Σ+(ν′),测量A1Σ+(ν′)的时间分辨激光感应荧光光谱,利用Stern-Volmer方程,得到振动能级ν″的总的弛豫速率系数kν(H2)。在H2和N2的混合气体中,总弛豫速率系数kν(H2+N2)与α(H2的摩尔配比)成直线的关系,其斜率为kν(H2)-kν(N2),而截距为kν(N2)。对于ν″<18主要发生单量子弛豫(Δν=1)过程,kν(H2)和kν(N2)与振动量子数ν″均成线性增加关系。对于ν″≥18,多量子弛豫(Δν≥2)过程及共振振动-振动转移起重要作用。对于RbH(ν″=21)+N2(0),测量ν″=16的布居数时间演化轮廓,在20μs内有一个锐锋,在100～200μs内有一个较低的宽峰,锐锋相应于RbH(ν″=21)+N2(0)→RbH(ν″=16)+N2(1)的共振转移过程,而宽峰是由相继的单量子过程产生的。

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 A 1Σ＋（ν′）→Х 1Σ＋（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） vs α（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.