Rb-He光学碰撞中精细结构分支比的测量

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

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(rνes)Δ(Δ=ν-rνes)。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-180cm-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)×10-17cm2,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。

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＋hv→Rb（5PJ ）＋ He, where the pulsed laser frequency v is tuned in the wings of the Rb resonance transitions. The authors defined the detuning △ to he vv（D2）（△〉0） for laser frequency highter than that of RbD2 transition and to be v-u（D1）（△〈O） for v lower than the RbD1 transition. As RbHe molecular states are correlated to the two 5^2 PJ states, there is some likelihood that the molecule will dissociate into 5^2 P1/2 or 5P3/2 state. The dissociation results in a nonuniform distribution of atomic RbSPJ states. The branching ratios are defined as n1 In2 , 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→SP1/2 ）[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 RbSP multiplet. A rate equation analysis of the pressure dependence was yielded. The branching ratios and cross sections for eollisional 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 cm^2 was measured from wing excitation, and the result is consistent with the cross section obtained from resonant excitation of the RbSPI state. The measurements show a strong sensitivity to interatomic potentials and to nonadiabatic effects in dissociation dynamics.