Transitions between Rydberg states of diatomic molecules in slow collisions with atoms

A close analytic representation has been found for the Green function of highly excited diatomic molecule in the framework of the multichannel quantum defect method. This expression has been used to describe the potential energy surfaces of the quasi-molecule X ₂ ^* +A. The specific behaviour of the terms of this system has been studied as a function of the angular orientation of the moleculeX ₂ and of the distanceR between the molecule and atomA. The terms have been found to have quasi-crossings responsible for the transitions when particles suffer collision. Some terms located near the continuous spectrum boundary, when the distance varies, cross the spectrum boundary and pass into auto-ionization state. Calculations have been made for the system H ₂ ^* +B, whereB is an inert gas atom. Cross-sections of the vibrational transitions occurring under slow atom-molecule collisions have been evaluated.