Collisionhyphen;induced transitions between molecular hyperfine levels: Quantum formalism, propensity rules, and experimental study of CaBr(Xthinsp;2Sgr;+)+Ar

摘要

The general quantum treatment of collisions of a2Sgr;+molecule with hyperfine structure is presented. The recoupling technique introduced by Corey and McCourt into the field of molecular collisions lsqb;J. Phys. Chem.87, 2723 (1983)rsqb; allows us to represent hyperfinehyphen;statehyphen;resolved tensor opacities, and hence cross sections, in terms of the corresponding nuclearhyphen; and also electronhyphen;spinhyphen;free quantities. The formalism also predicts (independent of the dynamical limit) that the largestFrarr;Fprime;cross sections will be those for which Dgr;F=Dgr;J, a rule well known for radiative transitions. Hyperfinehyphen;statehyphen;resolved scattering involving collisions of CaBr(Xthinsp;2Sgr;+) with Ar is also studied here experimentally by electric quadrupole state selection and cw dye laser fluorescence detection. The relative finalFprime;distributions were determined for theN=3,erarr;N=5,eandN=2,erarr;N=1,ecollisional transitions. These results clearly exhibit the Dgr;F=Dgr;Jpropensity rule. Moreover, theFprime;distributions were predicted with nearly quantitative accuracy using our previously determined CaCl(Xthinsp;2Sgr;+)hyphen;Ar tensor opacities. By contrast, theMJhyphen; randomization model, first proposed to treat the influence of hyperfine structure in atomic collisions, is shown to disagree with both our experimental data and theoretical predictions.