The2Πgshape resonance of the electron-acetylene scattering system: an ab initio treatment

The Feshbach formalism is applied to the calculation of polyatomic C 2 H 2 - in its 2 Pi g ( pi 4 u pi g ) resonance state. The discrete component of the resonance state as well as the width are calculated with a slightly modified configuration-interaction method; the resonance is thereby stabilised by increased nuclear charges. Integral cross sections for the elastic and vibrationally excited channels are calculated within the boomerang approximation. The results are consistent with corresponding experimental data. The cross sections exhibit a broad and structureless hump in contrast to the well known oscillatory cross sections of the isoelectronic e-N 2 scattering system ( Pi g symmetry). The comparison of the present results with previous calculations on the 2 Pi g resonance of N 2 - explains the differing features in the cross sections. The influence of technical variations on the location and width of the resonance as well as on the cross sections will also be discussed.