Penning ionization of the CO2 molecule by He*(2 1S) metastable atoms

This paper deals with an electron spectroscopy study of the Penning ionization of the CO2 molecule by helium atoms excited in the singlet metastable 2 1S state. The X, A, B and C electronic states of the CO2+ ion were identified in the electron energy spectrum obtained. A negative energy shift was measured for all these states. The ratio between the ionization cross sections of A and B electronic states was also measured. These A and B states were respectively favoured in the orthogonal and collinear approaches. Our results showed that, when the system switched from the orthogonal to the collinear direction, the attractive character of the He*-CO2 system was increased and the Penning ionization cross section became larger. One can explain these observations by the s-p hybridization of the helium 2s orbital occurring during the approach of the CO2 target. (author)