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

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Abstract
Angular distributions of autoionisation electrons from Ne(2p43s2)1D due to He++Ne collisions at 2 keV were measured in coincidence with the scattered projectiles and compared with those of electrons from He(2p2)1D, 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=2.4a0. 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=2.4a0. A quantitative estimate of the energy separations between Sigma , Pi and Delta potential curves correlating to He++Ne(2p43s2)1D indicates that a rotational coupling between these curves is responsible for the decoupling of electronic and nuclear motion at R approximately 2.4a0.