Theory of collision induced rotational energy transfer in the Π-state of diatomic molecules

It is suggested that an interaction not being invariant about the internuclear molecular axis is useful for the description of rotational excitation of diatomic molecules in the electronic Pi -state. In the framework of the helicity-basis of angular momentum a complete scattering theory qualified for numerical use is presented. Collision induced excitation by rare gases, Sigma - and Pi -state molecules, are treated separately. Special attention is paid to polarization phenomena. The connection with the usual angular momentum coupling scheme is given explicitly.