Excitation of atoms by electron impact near threshold

Abstract

A crossed beam apparatus for the measurement of excitation cross sections by electron impact for atomic hydrogen and the rare gases has been built which includes a high intensity long-channel beam source producing beam densities of the order of 1011 atoms/cm3. The atom beam was crossed by an energy selected electron beam with a full width at half maximum of about 100 meV, produced by a cylindrical electron monochromator.

The excitation function of the 2s state in atomic hydrogen and of the 4p5 5s states in krypton and the 5p5 6s states in xenon has been measured.

In the case of atomic hydrogen, the metastable 2s-atoms were detected by observing the Lyman-α photons emitted as a result of quenching in an electric field. Absolute values for the cross section were obtained by normalizing to the close-coupling calculations of Burke et al. The resonance structure at 11.7eV, which is a superposition of 1S and 3P resonances predicted by Burke at al, has been detected.

The excitation function of the first excited levels of krypton and xenon with the configuration 4p5 5s and 5p5 6s respectively has been measured by observing the ultraviolet photons from the decay of these states. In the threshold region, the excitation functions are found to be dominated by resonances. Comparison is made with other experimental results.