Basis representations for atomic collision problems: application to He_ + He*, _[Sigma]+g, two-state calculation

The coupled equations for the heavy-particle motion in atomic collisions are reviewed with emphasis on the transformation of the equations between different basis representations, in particular the adiabatic and diabatic representations. The application to the two-state approximation neglecting angular coupling is made and the required matrix elements and methods of evaluating these matrix elements are discussed; the various coupling terms are examined. Elastic and inelastic transition cross sections are calculated for collisions between metastable helium, He(1s2s,3S), and ground state helium. The inelastic transition He(1s28,3S) ---> He(1s2p0,3P) can occur in this collision due to the avoided crossing of the lowest two adiabatic 3 sigma, ^ +g potential curves for He2. The close coupling results are compared to results obtained using the adiabatic and diabatic decoupling approximations and the distorted wave approximation