(e,2e) ionization of helium and the hydrogen molecule: signature of two-centre interference effects

Abstract

Relative (e,2e) triply differential cross sections (TDCS) are measured for the ionization of the helium atom and the hydrogen molecule in coplanar asymmetric geometry at a scattered electron energy of 500 eV and ejected electron energies of 205, 74 and 37 eV. The He experimental results are found to be in very good agreement with convergent close-coupling calculations (CCC). The H2 experimental results are compared with two state-of-the-art available theoretical models for treating differential electron impact ionization of molecules. Both models yield an overall good agreement with experiments, except for some intensity deviations in the recoil region. Similar (e,2e) works were recently published on H2 with contrasted conclusions to the hypothesis that the two H nuclei could give rise to an interference pattern in the TDCS structure. Murray (2005 J. Phys. B: At. Mol. Opt. Phys. 38 1999) found no evidence for such an effect, whereas Milne-Brownlie et al (2006 Phys. Rev. Lett. 96 233201) reported its indirect observation. In this work, based on a direct comparison between experimental results for He and H2, we observe an oscillatory pattern due to these interference effects, and for the first time the destructive or constructive character of the interference is observed, depending on the de Broglie wavelength of the ejected electron wave. The experimental finding is in good agreement with the theoretical prediction by Stia et al (2003 J. Phys. B: At. Mol. Opt. Phys. 36 L257).

Ionisation differential cross section measurements for N2at low incident energy in coplanar and non-coplanar geometries

“…N 2 is the lightest diatomic molecule apart from H 2 that can easily be studied, since a molecular beam of N 2 can be delivered to the interaction region from a gas needle. H 2 has been extensively investigated both experimentally and theoretically [3][4][5][6][7], leading to considerable progress in understanding the dynamics of the ionizing collision with a molecular target. Models of the interactions include both time-independent studies using distorted wave calculations [3], as well as time-dependent models that use close-coupling techniques [4].…”

“…Models of the interactions include both time-independent studies using distorted wave calculations [3], as well as time-dependent models that use close-coupling techniques [4]. These models have been tested by experiment in both high and low energy regimes, under a wide variety of kinematic conditions [5][6][7].…”

Strong Molecular Alignment Dependence ofH2Electron Impact Ionization Dynamics

“…In this context, a large number of studies have been performed on H 2 which is the most simple and fundamental molecular system. Most of the previous ðe; 2eÞ experiments were done under random orientation conditions, thus neglecting effects due to the molecular alignment (see, e.g., [5,6,[8][9][10][11][12]). As a result, versatile and important information on the collision dynamics is missing.…”

Fivefold differential cross sections for the ionization of aligned hydrogen molecule by electron and positron impact

“…The fully differential cross section (FDCS) contains the complete information of an ionization process. Recently, attempts have been made both experimentally [1][2][3][4] and theoretically [3,[5][6][7][8][9][10][11][12][13][14][15][16][17] to get the FDCS for the ionization of simple diatomic hydrogen molecule by charged particle impact. In the case of diatomic molecules, the two-center geometry of the nuclear field can give rise to interference effects.…”