Angular correlation between autoionisation electrons from Ne(2p43s2)1D and scattered ions in He++Ne collisions

Angular distributions of autoionisation electrons from Ne(2p 4 3s 2 ) 1 D due to He + +Ne collisions at 2 keV were measured in coincidence with the scattered projectiles and compared with those of electrons from He(2p 2 ) 1 D, measured by Kessel et al. (1979). A theoretical analysis of such angular electron correlations in terms of a density-matrix description is given. The authors find that the Ne excitation occurs in a nearly pure m=0 sublevel with respect to an axis in the scattering plane which coincides with the internuclear line of the collision partners on the outgoing part of the trajectory at a separation of R approximately=2.4a 0 . This is interpreted as being due to an excitation at small R by a radial coupling of two Sigma -potential curves, followed by a rotation of the quasimolecule as a whole up to R approximately=2.4a 0 . A quantitative estimate of the energy separations between Sigma , Pi and Delta potential curves correlating to He + +Ne(2p 4 3s 2 ) 1 D indicates that a rotational coupling between these curves is responsible for the decoupling of electronic and nuclear motion at R approximately 2.4a 0 .