The Energy Losses Accompanying Ionization and Resonance in Mercury Vapor

Abstract

Energy Losses Accompanying Radiation and Ionization in Mercury Vapor.—To make possible a direct determination of the distribution of electron energies after impact with vapor molecules, a special tube was constructed in which the usual grid was replaced by two diaphragms each pierced with only a single hole. These divide the tube into two chambers which can be maintained at different pressures, the one in which the collisions take place being kept at a sufficiently high pressure and the other, in which the energies of the electrons after the collisions are measured, at a very low pressure by the use of liquid air. The source of electrons was an oxide-coated platinum foil heated by radiation from a tungsten filament, and energy distribution curves were obtained for a given accelerating potential by recording the electron current as a function of the retarding potential. These curves show that below 4.9 volts the collisions are elastic but that at higher voltages energy losses of 4.9, 5.7 or 6.7 volts may occur. For example, with an accelerating field (corrected) of 9 volts, breaks occur for retarding potentials of about 2.3, 3.3 and 4.1 volts, the curve being approximately horizontal between breaks. When ionization is produced, however, the electron loses all its energy, even though this much exceeds the ionizing potential, 10.4 volts, and the electron freed by the ionization also seems to have practically no energy. The 6.7 volt type of radiating collision is not probable unless the energy of the colliding electron exceeds 8.5 volts, but it becomes far more prominent than the 4.9 volt type above 10 volts. Comparison with spectroscopic and photoelectric data. The observed radiating potentials correspond to the known absorption lines $\lambda \lambda 2536$ (4.9 volts), 2330 (5.3), 2140 (5.9) and 1849 (6.7). Apparent discrepancies between these results and photoelectric data are discussed but the explanation is not yet clear.