Autoionization process in the Penning ionization of the CO molecule by Ne∗ (3P0, 3P2) metastable atoms

Penning ionization electron spectroscopy of the CO molecule by Ne∗ (3P2, 3P0) metastable atoms is reported. An extensive vibrational excitation of the electronic ground state X2Σ+ of the CO+ ion is observed. The measured angular distribution of the electrons corresponding to the first vibrational states (ν = 0−1) is anisotropic, while that of the higher levels is isotropic. A quasi-resonant excitation transfer process, leading to excitation of the molecular target into an intermediate autoionizing Rydberg state, is proposed to explain the discrepancy between the Franck-Condon factors and the observed excited vibrational levels of the X2Σ+ state.