Ionization in coplanar symmetric (e,2e) experiments of N2 and CO at intermediate energies.

Abstract

Measurements of the triple differential cross sections in coplanar symmetric energy sharing geometry for the two isoelectronic molecules ${\mathrm{N}}_{2}$ and CO are presented between 90 and 400 eV incident energy. At 400 eV, our results are compared to those of previous (e,2e) experiments done in other geometries and to photoionization data. At this incident energy, a comparison is also made with the plane wave impulse approximation (PWIA). Our calculations show that this does not perfectly describe the measured cross sections. Measurements made over an extended angular range, 30\ifmmode^\circ\else\textdegree\fi{}--120\ifmmode^\circ\else\textdegree\fi{}, present two maxima: that at large angle results from backscattering of the projectile prior to ionization of the target and is not explained by the PWIA. As energy is decreased, as for atoms, the relative importance of the low angle peak diminishes and that of the large angle peak increases: we then lack an adequate theoretical model and only comparison with data obtained for atomic targets under similar kinematical conditions is possible. Our high energy resolution permits the observation of several satellite structures for both target molecules, in particular for CO. At 400 eV, the assignment of these to different residual ion primary hole states correlates with the forms of the angular distributions. \textcopyright{} 1996 The American Physical Society.