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The light excited when protons or H₂⁺ ions pass through hydrogen or helium with kinetic energies of 2000 ev has been observed. Contamination of the beam by stray particles has been eliminated by electrostatic deflection and magnetic mass separation. The light is almost entirely due to the Balmer spectrum. Relative cross sections for the excitation of H_α by protons and H₂⁺ impinging on H₂ and He have been determined.
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Ernest J. Dieterich (1956) studied this question.
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