Collision Matrix Elements near a Pseudocrossing of Potential Energy Curves

The behavior of the matrix element of the collision operator, d/dR, between adiabatic states with variations in R, the internuclear separation, is studied qualitatively for diatomic molecules. These matrix elements often have a maximum or a zero near the pseudocrossing of the two adiabatic potential energy curves. Effects of these extremes of behavior on cross sections are considered and limits on the validity of approximations which use R-independent orbitals are developed. Finally, the effect of a second pseudocrossing on these matrix elements is analyzed.