The inelastic scattering of slow electrons in gases.—III

Abstract

The subject of electron scattering in gases has received considerable attention within the last four years, and the very interesting results obtained have greatly assisted the wave mechanical study of collision processes. The investigation of the angular distribution of the scattered electrons has proved particularly valuable. The elastic scattering has been studied systematically in a number of gases over a wide range of velocities and angles of scattering. The inelastic scattering, however, has not been so exhaustively studied, the measurements in general being limited to small angles of scattering (less than 60°) and to high velocities of impact (above 50 volts). Recently Hughes and McMillen have investigated the inelastic scattering of 25-, 35-, and 50-volt electrons in hydrogen for angles of scattering between 10° and 165°; the curves were found to rise slightly at large angles. Tate and Palmer, and Hughes and McMillen have measured the angular distribution of electrons which have been ejected from the atom with only a few volts energy; the curves obtained were on the whole fairly flat, although the latter observers find in some experiments sharp peaks at large angles. In two previous papers, the angular distribution of inelastically scattered electrons which have lost a discrete amount of energy were investigated in several gases for large angles of scattering, and for electrons with energies greater than about 40 volts. At large angles, diffraction maxima and minima were found similar to those which occur for the elastic scattering, although the similarity between the two sets of curves was less marked at the lower velocities. The present work was therefore undertaken to investigate this more interesting region. While the previous apparatus proved entirely satisfactory for the purposes for which it was used, it was found that at low velocities troubles due to intensity and "background" indicated that it was desirable to construct an apparatus in which every possible precaution was taken to avoid these difficulties.