Relative differential electron impact cross sections sigma ( theta ) for elastic and inelastic scattering in mercury have been measured. The sigma ( theta ) are normalized to the optical oscillator strength for the 61S0-61P1 transition and put on an absolute scale. Results are presented at 15, 25, 35, 40, 50, 60 and 100 eV for elastic scattering and the 61P1 excitation. In addition the 63P1, 71S0 and 71P1 excitation sigma ( theta ) are presented at 60 eV. The angular ranges are from 2' for inelastic and from 10' for elastic scattering, up to 150'. Results are compared with the other experimental and theoretical data. Comparison with the relativistic calculations is given by Srivastava et al. in the following paper (ibid., vol.26, no.5, p.1025-30 (1993)).

The resonant metastability-exchange process is used to obtain a metastable atom beam with intrinsic properties close to those of a ground-state atom nozzle beam (small angular aperture, narrow velocity distribution). The estimated effective source diameter (15 µm) is small enough to provide at a distance of 597 mm a transverse coherence radius of about 873 nm for argon, 1236 nm for neon and 1660 nm for helium. It is demonstrated both by experiment and numerical calculations with He*, Ne* and Ar* metastable atoms, that this beam gives rise to diffraction effects on the transmitted angular pattern of a silicon-nitride nano-slit grating (period 100 nm). Observed patterns are in good agreement with previous measurements with He* and Ne* metastable atoms. For argon, a calculation taking into account the angular aperture of the beam (0.35 mrad) and the effect of the van der Waals interaction—the van der Waals constant C3 = 1.83+0.1−0.15 au being derived from spectroscopic data—leads to a good agreement with experiment.

An atomic interferometer using the longitudinal Stem-Gerlach effect has been constructed. A thermal beam of metastable hydrogen atoms has been used to test the apparatus. Interference patterns have been obtained. The visibility of the fringes is limited by the velocity spread of the beam. The observed patterns are in good agreement with that predicted from the actual velocity distribution.

Surface-induced transitions between Zeeman sub-levels of metastable neon atoms traversing a micro-slit copper grating are investigated. The quadrupolar part of the surface van der Waals interaction suddenly perturbs the evolution of the Zeeman sub-levels in a magnetic field B, giving rise to van der Waals -Zeeman transitions. Exothermal inelastic transitions are identified by the related deflection γ. In a diagram (γ, B 1/2 ) the location of the inelastic peaks is fitted by straight lines of slopes proportional to |∆m| −1/2 , where ∆m is the magnetic number change.