The Ionization of Hydrogen by Electron Impact as Interpreted by Positive Ray Analysis

T. R. Hogness and E. G. Lunn
Phys. Rev. 26, 44 – Published 1 July 1925
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Ions produced in hydrogen by electron impact.—Using an apparatus previously described in which positive ions formed by impact of electrons of definite energy (V1+V2) are accelerated and then deflected magnetically around a semi-circle into a Faraday cylinder, the relative numbers of ions of types H+, H2+ and H3+ were measured as a function of pressure from <0.1×104 mm to.006 mm, and also as a function of impact energy (V1+V2) to 60 volts. At low pressures only H2+ ions are formed; as the pressure is increased the percentage of H3+ increases in proportion to the pressure. In the apparatus used, the percentage of H+ increased with pressure but did not exceed 4 percent, while the percentage of H3+ ions reached 60. These results confirm the conclusions of Dempster and Smyth that the primary process in the ionization of hydrogen is the ionization of the molecule without dissociation. The previously measured ionization potential at 16 volts (confirmed in this work) is that for the formation of H2+. H3+ also appears at this potential, but as a result of a secondary process. It appears that the H2+ ion is readily dissociated by collision and that the H+ ion formed may unite with the H2 molecule collided with or with some other molecule to form H3+. The interpretation of ionization potentials reported by other observers is discussed in the light of these results.

Ions produced in helium containing hydrogen, by electron impact.—The percentage of H+ ions found was greater even than the percentage of H2+, while no H3+ ions were observed. Evidently the primary ions H2+ are readily dissociated by impact with He atoms. Evidence was found for the ions HeH+ and also for an ion with me=6, perhaps HeH2+.

  • Received 9 February 1925


©1925 American Physical Society

Authors & Affiliations

T. R. Hogness and E. G. Lunn

  • Department of Chemistry, University of California

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Vol. 26, Iss. 1 — July 1925

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