Rotationally inelastic collisions between a diatomic molecule in a 2Σ+ electronic state and a structureless target

Abstract

We present the full close‐coupling formulation of the collision between a diatomic molecule in a ²Σ⁺ state and a structureless target. Due to the possibility of transitions which are inelastic in the parity index of the doublet states, the scattering displays an additional degree of complexity not seen in rotationally inelastic collisions of ¹Σ⁺ molecules. The well‐known coupled states and infinite‐order‐sudden approximation techniques can be applied in a straightforward manner. The factorization and scaling relations between the various cross sections, which are valid in the energy sudden limit, are explored. These allow the entire matrix of cross sections, both parity conserving and parity violating, to be expressed in terms of the cross sections for parity conserving transitions out the lowest (J = 1/2) level. Within the sudden limit it is also possible to show that at large values of the total angular momentum, transitions which conserve the parity index of the molecular wave functions will be strongly favored, a propensity rule which has been seen in previous experimental studies of rotational relaxation in ²Σ⁺ molecules. If the doublet states are unresolved, the sudden scaling relations become identical to those derived previously for collisions of ¹Σ⁺ molecules.