No abstract

An expression is derived for the cross sections, Vj\ for the collision-induced relaxation of the multipole moments of an ensemble of excited atoms in a state of total angular momentum j. Various general sum rules are obtained for the &/ x \ as well as for the Kf x ' =aA x^ -cy^, the cross sections for reorienting collisions.For a j=l state, one obtains A^1* / A t {2) = $•. This result implies that the cross section for collision induced I Am I =2 transitions is always twice that for \Am\ = l transitions, independent of the assumed interaction potential. Absolute cross sections are obtained using the van der Waals collision model. Translational motion is treated in a classical linear path approximation. It is shown that the cross sections can be written in the form oj(#)where v is the relative velocity between the colliding atoms, D depends on the particular atoms and states considered, and