• ab initio calculations;
  • argon;
  • collision-induced transitions;
  • radicals;
  • rotational energy transfer


The behavior of Λ-doublet resolved rotational energy transfer (RET) by Ar collisions within the SH(X2Π, v′′=0) state is characterized. The matrix elements of terms in the interaction potential responsible for interference effects are calculated to explain the propensity rules for collision-induced transitions within and between spin–orbit manifolds. In this manner, the physical mechanisms responsible for the F1–F1, F2–F2, and F1–F2 transitions may be reasonably identified. As collision energy increases, the propensity for collisional population of the final e or f level is replaced by the e/f-conserving propensity. Such a change in propensity rule can be predicted in terms of energy sudden approximation at high J limit for the pure Hund’s case scheme.