Endothermal fine-structure transition of metastable argon atoms passing through a micro-slit copper grating

Abstract

The endothermal fine-structure transition ( 3 P2 → 3 P0 -175 meV) of metastable argon atoms traversing at a velocity of 1030 m/s a micro-slit copper grating the normal axis of which is set, in a first configuration, at 60 • with respect to the incident beam axis, is observed. The related differential cross-section (DCS) is sharply peaked at 60 • and its velocity dependence reveals the expected threshold at 900 m/s. In a second configuration, the grating is set at an angle of 43 • , allowing for a 7% transmission of the incident beam. Atoms elastically scattered by the corner edges of the grating slits are observed in the angular range 1 • -4 • and the elastic DCS is measured in relative values. In spite of such a widely unsuited geometry, the endothermal process still appears (with a magnitude 10 times smaller than before), because of the surface corrugation. The inelastic DCS is now peaked at 57.5 • with a width of about 6 • , as predicted from the corrugation angle distribution deduced from the inelastic DCS of metastable N * 2 molecules traversing the same grating.

Surface-induced vibrational excitation of metastable nitrogen molecules traversing a micro-slit copper grating: a probe of surface profiles

“…Then assuming a regular variation of α along the surface, a mean 2D profile of the slit walls can be derived. It is worth noting that the same profile is obtained when the fine-structure endo-energetic transition of metastable argon atoms (Ar * 3 P 2 → 3 P 0 ) is considered in place of the present vibrational excitations of N 2 * [19]. Moreover, the resulting profile appears to be the one expected from the technique (electro-deposition) used in the grating fabrication.…”

“…Actually, as has already been shown with argon metastable atoms traversing a grating of the same type [19], the surface of the slit walls is not planar. Here this is demonstrated in the following way.…”

“…A simple distribution function F(α) of the angle α between the reference plane and the local tangent plane has been determined in view of fitting both the present inelastic DCS (figure 1) and that obtained previously for the endo-energetic fine-structure transition ( 3 P 2 → 3 P 0 ) of argon metastable atoms traversing a copper grating of the same type, with an identical shape of the slit edges according to the manufacturer (Labelcomat), set at about the same position (θ G = 43 • ) [19]. This distribution is shown in figure 4(a).…”

Atom-wall interaction

“…This introduces in the principle extra quadrupole effects in the interaction, with the additional breaking of some usual symmetry rules. In the principle, this break of symmetry within the vicinity of the surface may enable previously forbidden transitions, analogous to those observed by andKaram et al (2002).…”

“…Anyhow, the strong angular selectivity of the process has permitted to observe this signature of vW anisotropy in various situations. The successful observation for metastable Ar and Kr atoms transmitted through a micro-slit was followed by a more efficient process associated to transmission through a nano-grating (Boustimi et al, 2001 b), by an extension to a molecular 49 specie (metastable N 2 ) , and even by the observation of the reverse endothermic metastability transfer (Karam et al, 2002).…”