A model study of vibrational excitation of carbon dioxide molecule by slow electrons: the role of wave packet sliding from the ridge

The method of an accurate calculation of vibrational excitation cross sections of a two-mode molecule by slow electrons within the framework of the local theory (the ‘boomerang’ model) is applied for a model study of the excitation of the symmetrical stretching vibrational modes of carbon dioxide in the two-mode approximation (i.e., only the symmetrical stretch and bending modes are included in the consideration). It is shown that the 'boomerang’ oscillations in the cross section are strongly suppressed due to the decay of the one-dimensional ‘boomerang' state caused by the anion wave packet sliding from the linear configuration ridge. Consequently, the bending motion in CO₂ molecule should to be taken into account even if only the processes without the final bending excitation are considered. A simple quasi one-dimensional model describing the system sliding from the ridge is put forward which treats this phenomenon as a decay of the initial wave packet via the series of diabatic resonant states related to unstable trajectory.