Lyman-Alpha Emission Induced by the Collisions of Electrons with Molecular Hydrogen

Abstract

The ratio of electron-impact cross sections of atomic and molecular hydrogen for production of uv radiation detected by an oxygen-filtered iodine-vapor-filled photon counter has been precisely measured in a modulated beam experiment. Using a filter 1.67 cm long with an oxygen pressure of 1 atm, the ratio of cross sections at 100 eV was found to be 4.05 ± 0.07. Using the known cross section for production of Lyman-alpha radiation from the hydrogen atom, the cross section for molecular radiation received by the detector was determined to be 1.48 (± 0.05) × 10−17 cm2.

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

“…Such a measurement requires accurate determination of the dissociative fraction. , Kauppila et al (1971) and Woolsey el ai. (1986) use;: this IIlt;lhuu iu l:IUSSCU-Ut;ams experiments to determine the Lyman-alpha cross section ratio for the excitation of hydrogen atoms to the dissociative excitation of hydrogen molecules.…”

“…The disso-ciative fraction follows from known ionization cross sections. Kauppila et al (1971) use a tungsten furnace and a quadrupole mass filter. The dissociative fraction measured by the quadrupole mass filter is corrected for mass discrimination effects.…”

“…Carriere and de Heer ( 1972) measure the contribution of radiation of molecular origin transmitted through a LiF-02 filter and use this number to obtain the H 2 (H I Ly-a) cross section based on the CUV cross section of and nnnn ptnl (1962). Kauppila et al (1971) measure a ratio of 4.05 ± 0.07 between the CUV cross section and the H I(Ly-a) photoemission cross section for 100 eV electrons on atomic hydrogen. Using this number and the H l(Ly-a) cross section from Long et al (1968) they calculate the CUV cross section at 100 eV.…”

“…Using this number and the H l(Ly-a) cross section from Long et al (1968) they calculate the CUV cross section at 100 eV. Mumma and Zipf (1971a) use the ratio between the CUV and the atomic cross section from Kauppila et al ( 1971), the ratio between the dissociative and the CUV cross section from and Carriere and de Heer ( 1972), and the atomic cross section from Long et al (1968) to find the H 2 (H I Ly-a) dissociative cross section. They use this number to absolutely calibrate their H 2 (H I Ly-a) optical excitation function.…”

Dissociative Excitation of Vacuum Ultraviolet Emission Features by Electron Impact on Molecular Gases. I. H2 and O2

“…Kauppila et al 13 have redetermined the ratio of the cuv cross section (u ouv ) to the cross section (UA) for excitation of Lyman-alpha photons by electron impact on hydrogen atoms. They used an experimental apparatus similar to Fite and Brackmann's2 and they have reduced the error substantially.…”