Rb-He光学碰撞中精细结构分支比的测量

脉冲激光激发Rb＋He混合系统, 激光频率（ν）调离Rb（5Ｓ1/2）→Rb（5PJ）共振频率（νres）Δ（Δ＝ν-νres）。研究了光学碰撞Rb（5S1/2）＋He＋hν→Rb（5PJ）＋He转移过程。激光激发RbHe分子态。RbHe激发态解离到5P1/2或5P3/2态，其布居数密度分别为n1和n2,定义分支比为n1/n2。为得到分支比，在-180 cm-1＜Δ＜200 cm-1范围内测量了I（D1）（5P1/2→5S1/2）与I（D2）（5P3/2→5S1/2）的相对时间积分强度比R，解速率方程组，得到一个与气压成线性关系的直线方程，从该直线的截距及斜率得到5P1/2→5P3/2的碰撞转移截面及分支比, 在D2线蓝翼，分支比随失谐量Δ的增加而增加到0.2。在D1线红翼分支比近似为40而与失谐量无关。从翼激发测量得的精细结构碰撞转移截面为（1.1±0.3）×10-17 cm2, 与从共振激发得到的截面值是一致的。测量结果表明, 原子相互作用势和非绝热效应在分子解离动力学中起关键作用。

Measurement of Fine-Structure Branching Ratios for Rb-He Optical Collisions

Experimental ratios of branching in the fine-structure levels of the Rb5P multiplet, as a consequence of an optical collision with He, are reported. The process studied is Ｒｂ（５Ｓ１／２）＋Ｈｅ＋ｈν→Ｒｂ（５ＰＪ）＋Ｈｅ, where the pulsed laser frequency ν is tuned in the wings of the Rb resonance transitions. The authors defined the detuning Δ to be ν-ν(Ｄ２)（Δ＞０） for laser frequency ν highter than that of RbD2 transition and to be ν-ν（Ｄ１）（Δ＜０） for ν lower than the RbD1 transition. As RbHe molecular states are correlated to the two ５　２ＰＪ states, there is some likelihood that the molecule will dissociate into ５ ２Ｐ１／２ or 5P3/2 state. The dissociation results in a nonuniform distribution of atomic Rb5PJ states. The branching ratios are defined as n1/n2, where n1 and n2 are densities of the 5P1/2 and 5P3/2 states dissociated. To determine experimentally the relative cross section for scattering into the two fine-structure states, the relative time-intergrated intensities of the resulting Rb emission lines, I(5P3/2→5P1/2)［Ｉ（Ｄ２）］ and Ｉ（５Ｐ１／２→５Ｐ３／２）［Ｉ（Ｄ１）］, were measured. The ratios are determined by detunings from about 200 cm-1 in the blue wing to -180 cm-1 in the red wing of the Rb5P multiplet. A rate equation analysis of the pressure dependence was yielded. The branching ratios and cross sections for collisional 5P1/2→5P3/2 transition were obtained from the slope and intercept. The blue-wing branching ratios show a detuning-dependent approach to limit of 0.2. The branching was found to be very large (～40) in the red wing, irrespective of the detuning. Fine structure changing cross section (1.1±0.3)×10-17 cm2 was measured from wing excitation, and the result is consistent with the cross section obtained from resonant excitation of the Rb5PJ state. The measurements show a strong sensitivity to interatomic potentials and to nonadiabatic effects in dissociation dynamics.