Absolute Measurement of2SAtom Production by Dissociative Excitation of Molecular Deuterium

Abstract

We have measured the cross section for production of metastable (28) atoms by the process of dissociative excitation of molecular deuterium by electron impact;. The measurement includes the quantitative evaluation of detection efficiency, density, and geometrical factors necessary to establish an absolute scale on a purely experimental basis. The method depends on the application of an rf field at the Lamb-shift frequency (1059 MHz) to quench the metastables at the point of excitation. The radiation induced by the applied field is isotropic so that the absolute cross section depends on a simple solid-angle correction. The cross sections at 23. 8 and 39.1 eV are 2. 97 x 10-~a nd 3.40 x 10-~8 cm2, respectively, vrith a probable error estimated to be + 14%. The energy dependence of the cross section eras also measured from threshold to 500 eV.

Electron-impact cross sections for deuterated hydrogen and deuterium molecules

“…These cross sections can, however, be measured by an indirect method. The D(2s) atoms are caused to radiate by the application of an electrostatic field [95] or rf-field [96] (at 1059 MHz frequency) across the observation region. First, the measurements are carried out under zero quenching field conditions.…”

“…The electron-impact D Lyman-α emission cross sections for 2p → 1s transition have been measured by Becker and McConkey [91], Vroom and de Heer [95], Möhlmann et al [108] and Ciocca et al [101] whereas the cross sections for 2s → 1s D Lyman-α transition have been measured by Vroom and de Heer [95], Cox and Smith [96] and Möhlmann et al [108]. In the case of D Lyman-α 2p → 1s emission, Ciocca et al [101] reported the total emission cross sections along with those for slow and fast components, which correspond to the line center and the wings, respectively.…”

Photoemission Cross Sections for Atomic Transitions in the Extreme Ultraviolet due to Electron Collisions with Atoms and Molecules

“…They normalize on the Born approximation taking cascade into ac-count, but they apply no correction for the polarization of the emitted radiation. Cox and Smith (1972) measure an optical excitation function of the CUV cross section on a relative scale.…”

Vacuum Ultraviolet Excitation of H(2p) by Electron Impact on H2

“…This should not affect the shape of the function, however, as it has been shown by Vroom and de Heer ( 1 9 6 9~) and by Cox and Smith (1972) for D, that the 2s and 2p excitation functions are similar in shape.…”

“…Finally, a relevant comparison may be made with the work of Cox and Smith (1972) who have made similar measurements using D2. They observed the countable UV radiation at right angles to the electron beam using a MgF-0, filter combination and found a broad maximum in the excitation function around 70 eV.…”