Rotationally Inelastic Collisions between a Molecule in a (2s+1) Sigma Electronic State and an Open-Shell Target: General Quantum Analysis and Experimental Measurement of State-Resolved Cross Sections for CaCl(X2 Sigma+) + NO(X2 p

摘要

Collision induced transitions between the multiplet and/or rotational levels of an open-shell molecule scattered by an atomic target arise because the orbital motion of the collision partners couples with the nuclear rotational, electronic orbital, or electronic spin angular momenta of the molecule. The magnitude of this coupling reflects the anisotropy of the atom-molecule electrostatic potential surface (or surfaces, as in the case of collisions involving molecules in Pi electronic states). The general quantum treatment for the scattering of molecules in 2S + 1 Sigma electronic states by open-shell 2S atoms is investigated, with particular emphasis given to the influence of the open-shell character of the atomic perturber on the collisional propensity for conservation of the e/f molecular symmetry index. The molecule-state-resolved cross sections are expressed as a sum of spin-independent and spin-correlated terms. The spin-independent term is formally equivalent to the cross section for state-resolved transitions in a 2S + 1 Sigma-state molecule upon collision with a structureless target. The spin-correlated term is due solely to the electrostatic exchange forces arising from the open-shell nature of both the molecule and the atomic target. Recently calculated CaCl(X2Sigma(+))-Ar cross sections are used to investigate the extent to which e/f conservation depends on the relative magnitudes of these two contributions. Experimental state-to-state rotationally inelastic cross sections for the scattering of CaC1(X2Sigma+) by the open-shell NO(X2Pi) molecule are presented and analyzed by means of this formalism.