J. Phys. II France
Volume 7, Numéro 11, November 1997
Page(s) 1543 - 1554
DOI: 10.1051/jp2:1997202
J. Phys. II France 7 (1997) 1543-1554

Excitation Transfer Process in Penning Ionization of the CO Molecule by Helium Atoms in Singlet Metastable State

B. Lescop, M. Ben Arfa, G. Le Coz, M. Cherid, G. Sinou, G. Fanjoux, A. Le Nadan and F. Tuffin

Laboratoire de Physique des Collisions Électroniques et Atomiques, Faculté des Sciences et Techniques, Université de Bretagne Occidentale, 6 avenue Le Gorgeu, B.P. 809, 29285 Brest Cedex, France

(Received 13 December 1996, revised 10 June 1997, accepted 16 July 1997)

Penning ionization electron spectroscopy of the CO molecule by He * ( 21S) metastable atoms is studied. Vibrational populations are reported for the three energetically accessible states of the CO + ion (X $^2\Sigma^+$, A 2 $\Pi$ and B $^2\Sigma^+$). An obvious discrepancy is observed between the excited vibrational levels of the X $^2\Sigma^+$ state and the calculated Franck-Condon factors. This result is attributed to an excitation transfer process via Rydberg vibrational progression converging to the CO + (D 2 $\Pi$) ionic state in agreement with the recent observations by fluorescence of neutral dissociate states. The presence of electrons coming from the well-known $\sigma$ shape resonance is not excluded.

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