Rb(7S-5D)-H_2,He能量转移截面与温度的关系

Temperature Dependence of Cross Sections for Energy Transfer Processes of Rb(7S-5D)-H_2,He

脉冲激光双光子激发Rb(5S)态到Rb(5D)或Rb(7S)态,在样品池条件下,利用原子荧光光谱方法测量了Rb(7S-5D)-H2,He碰撞能量转移截面与池温的关系。利用三能级模型的速率方程分析。通过测量在不同H2或He密度下的直接荧光与转移荧光的时间积分强度比,在353～493K温度范围内得到了Rb(7S-5D)-H2,He的反应与非反应碰撞能量转移截面。对于Rb(7S)+H2→Rb(5D)+H2,其转移截面随温度的增加而减小,而其逆过程的转移截面则随温度的增加而增加。对于与He的碰撞,在不同温度下7S-5D的转移截面均符合细致平衡原理,7S,5D态与H2的碰撞速率系数是反应与非反应速率系数之和,利用实验数据可以分别确定反应与非反应截面,7S态的平均反应截面与5D态平均反应截面之比约为1.5。Rb(7S)与H2的反应活动性大于Rb(5D)。

Rb vapor, mixed with H2 or He, was irradiated in a glass fluorescence cell with pulses of radiation from a YAG-laserpumped OPO laser, populating 5D or 7S state by two-photon absorption. The temperature dependence of the cross sections for 5D-7S transfer induced by collisions with He atoms and H2 molecules was determined using methods of atomic fluorescence. The resulting fluorescence included a direct component emitted in the decay of the optically excited state and a sensitized component arising from the eollisionally populated state. At the different densities, the authors have measured the relative time-integrated intensities of the components and fitted a three-state rate equation model to obtain the reactive and nonreactive cross sections for Rb（7S-5D） H2, He collisions. The cross sections of transfer for Rb（7S）＋ H2→Rb（SD）＋ H2 decrease with increasing T. The cross sections for 5D-＋7S increase with increasing T. At the different temperatures, the cross sections of transfer for （7S-5D）- He collisions coincide with the principle of detailed balance. The total transfer rate coefficients out of the 7S or 5D state for He were small. The total quenching rate coefficient out of the 7S or 5D state was much larger for H2. In the case of H2, the quenching rate coefficient corresponds to reaction and nonreactive energy transfer. In reaction of Rb（7S, 5D）＋ Hz→RbH＋H, the ratio between the reactive cross sections was found to be σ^- [Rb （7S） ＋ H2 ]/σ^- （ Rb （5D） ＋ H2 ] = 1.5. The relative reactivity with H2 was in an order of Rb（7S）〉Rb（SD）.