Efficiency of Excitation by Electron Impact and Anomalous Scattering in Mercury Vapor

The efficiency of excitation by electron impact of the 6.67 volt resonance level in the mercury atom has been studied as a function of the energy of the incident electrons. The electrons that have lost energy are separated out by a small retarding field and measured. The number of collisions is calculated from the experimentally determined value of the mean free path. The range covered is 0.4 volt from 6.67 to 7.07 giving a value for every 0.1 volt of the interval. The efficiency reaches a maximum of about 0.06 at 6.77 volts and then falls off to 0.04 at 7.0 volts.The number of electrons scattered elastically at large angles by mercury vapor as a function of their energy was measured. The energy range covered was from 2 to 10 volts in steps of 0.2 of a volt. Certain very definite singularities were found. These correspond to an increase in large angle scattering and occur most prominently at 4.9, 5.7, and 6.3 volts. A less prominent group of singularities was also observed at 9.6, 10.3 and 11.1 volts.