EXCITATION TRANSFER PROCESS IN PENNING IONIZATION OF THE CO MOLECULE BY HELIUM-ATOMS IN SINGLET METASTABLE STATE

Penning ionization electron spectroscopy of the CO molecule by He(2(1 )S) metastable atoms is studied. Vibrational populations are reported for the three energetically accessible states of the CO+ ion (X-2 Sigm a(+), A(2) Pi and B-2 Sigma(+)). An obvious discrepancy is observed be tween the excited vibrational levels of the X-2 Sigma(+) state and the calculated Franck-Condon factors. This result is attributed to an exc itation transfer process via Rydberg vibrational progression convergin g to the CO+ (D-2 Pi) ionic state in agreement with the recent observa tions by fluorescence of neutral dissociate states. The presence of el ectrons coming from the well-known a shape resonance is not excluded.