A distorted-wave study for core-excitation processes in CO2 by electron impact

In the present work, the distorted-wave approximation (DWA) is applied for the first time to study core-level excitations in molecules by electron imp act. More specifically, we have calculated differential and integral cross sections for the X(1)Sigma(g)(+)-->(1,3) Pi(u) (carbon 1s 2 sigma(g) --> 2 pi(u)) transitions in CO2 in the 320-800 eV incident energy range. The froz en-con generalized oscillator strengths (GOS) for the transition leading to singlet excited states calculated using both the DWA and the first Born ap proximation (FBA) at 1290 eV are also reported. Our calculated DWA GOS are in general 20% lower than the corresponding FBA, results which seem to indi cate that the FBA is not valid at that incident energy. Moreover, we have a lso calculated the ratios between the distorted-wave integral cross section s for the transitions leading to the triplet and the singlet excited states as a function of incident energy. The comparison of these data with the ex perimental ratio R(3A:1A) obtained by dividing the intensities of the autoi onizing electrons from the same excited states in the 320-800 eV range is e ncouraging. (C) 1999 Elsevier Science B.V. All rights reserved.