Experimental measurements are reported for the Penning ionization of an argon target by impact of metastable helium atoms. The energy spectra of the ejected electrons are obtained at a series of angles in the range 30° to 90°, and the intensities due to the different metastable states compared

2014 Les auteurs ont étudié le spectre en énergie des électrons éjectés au cours de l'ionisation Penning de l'azote moléculaire par les métastables de l'hélium. Un modèle, faisant intervenir la formation d'une quasimolécule, est proposé pour rendre compte de certaines anomalies dans l'ionisation Penning par l'état métastable 2 3S. Les auteurs suggèrent également la présence d'un état autoionisant de N2 qui aurait pour effet d'accroître la section efficace d'ionisation par l'état métastable 2 1S. Abstract. 2014 A study is reported of the ejected electron spectra resulting from Penning ionization of a molecular nitrogen target by impact of helium metastables. A model is proposed for ionization by the 2 3S metastable in which the formation of a quasi-molecular complex is invoked, and it is suggested that the presence of an autoionizing state of N2 leads to enhancement of certain cross sections for ionization by the 2 1S metastable.

Penning ionization of the H a molecule by the He'(2'S) metastable atom is studied. The energy shift is measured for the three observed X, A and B eiectronic bands of the residual HzO' ion. The absence of the vibrational structures is discussed in light of the known interaction potential surface of the He'-t120 complex. More altention is given to the X electronic band characterized by interference structures at high electron energy and an important angular dependence intensity.

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2014 Nous avons étudié l'ionisation Penning des gaz rares Ar, Kr et Xe par impact de métastables d'hélium et de néon. Nous avons déterminé les déplacements en énergie des pics correspondant aux différents processus d'ionisation. Nous confirmons la plupart des résultats antérieurs. Nous avons mis en évidence une dissymétrie et des structures du côté des basses énergies dans les pics électroniques correspondant à l'ionisation de Kr et Xe. Nous avons réalisé une étude de la distribution angulaire des électrons éjectés dans le domaine angulaire 20° à 90°. Le résultat essentiel et original de cette étude est la mise en évidence d'une dépendance de cette distribution angulaire en fonction du niveau de structure fine de l'ion créé.

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Penning ionization of the CO2 molecule by Ne* (3 3P2,0) metastable atoms is studied by electron spectroscopy. The recorded electron energy spectrum is dominated by an important vibrational progression that is decomposed over the nν1 and nν1+2ν3 vibrational series up to n=5. In addition, we observe a low-energy broad hump extending from 0.5 to 1.5 eV. The presence of this new feature is attributed to a non-van der Waals interaction between the colliding particles. Making the hypothesis that an ion–pair state channel opens during the collision, we are in a position to interpret the entire set of experimental results. We believe that the opening of this channel is responsible for the production of the CO2 molecule in an autoionized Tanaka–Ogawa Rydberg state.

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.