MQDT analysis of predissociation. I. A two channel problem with semiclassical scattering parameters

Diatomic predissocitaion (case I) is treated in the framework of the multichannel quantum defect theory (MQDT) by adapting the Child and Bandrauk formulation. Analytical expressions are given for the scattering parameters of a two channel problem in terms of WKB phase integrals and of crossing parameters. Resonances in scattering and photoabsorption spectra are identified as the points of steepest rise of an effective phase shift, and analytical expessions are derived for both linewidths and energy shifts. A sample calculation shows the effects of coupling with the B 3Σ−u state upon the partial elastic cross section of two oxygen atoms colliding in the 5Πu channel.