Autoionization process in Penning ionization of the CO molecule by helium atoms in triplet metastable state

Abstract

In this paper, we investigate the Penning ionization of the CO molecule by helium atoms in metastable states. The energy distribution spectrum of electrons related to the CO + (X 2 + ) ion state shows a deviation of the vibrational population from the predicted Franck-Condon factors. The angular distribution measurements exhibit an intensity increasing towards the backward direction for the v = 0 level, while the corresponding angular distributions of the higher vibrational levels (v = 2, 3 and 4) are isotropic. To explain these results, an excitation transfer process between the colliding particles is suggested. This gives rise to a CO molecule either in a doubly excited Rydberg state converging to CO + (D 2 ) or in the σ * quasi-bound state (shape resonance). Autoionization of the doubly excited state (CO * * ) leads to the population of vibrational levels which are forbidden by the Franck-Condon principle in the case of a direct processes.

Two-Dimensional Penning Ionization Electron Spectroscopy of CH2ClI and CH2ClCN

“…Because band S is clearly different from the normal Franck−Condon vibrational distribution for band 4, it may be related to the formation of a superexcited state of CH 2 ClI energetically close to the excitation energy of the He*(2 3 S) atom. Similar bands for specific molecules such as HCl, CO, etc. have been observed in the PIES.…”