Rotationally Induced Transitions in Atomic Collisions

Excitation effects due to rotational motion of the internuclear line during an atomic collision are considered in the two-state approximation. These effects are governed by a pair of first-order differential equations which couple adiabatic levels of different angular momentum (e.g., $\sigma$ to $\pi$ transitions), which actually do cross. The equations are cast in such a form that the solution for rotational excitation may be expressed in terms of the well-known Landau-Zener solution. It is found, however, that application of these results to a real collision suffers from defects which are worse for the case of rotational excitation than for ordinary Landau-Zenner transitions. The coupled differential equations are then solved numerically to document the shortcomings of the Landau-Zener approach to a real collision and to present cross-section results which are free from these defects.