Collisions of Electrons with Hydrogen Atoms. III. Elastic Scattering

The cross section for elastic scattering of electrons of less than 10-ev energy by free hydrogen atoms has been measured. The experimental approach was similar to that used by Bederson, Malamud, and Hammer in that a dc electron beam crossed an atomic hydrogen beam, which was chopped at a low frequency, and the signal was derived from the electrons scattered by the particles in the neutral beam. The electrons scattered by the beam were identified by their signal's appearing at the modulation frequency and at a specified phase. Direct measurements of the ratio of cross sections of the hydrogen atom and the molecule were made, and absolute values for the atomic cross section were obtained from knowledge of the absolute molecular cross section. The experimental results agree with theory.