The Motion of Electrons in Hydrogen and Helium

Mobilities of electrons in H₂ and He at 760 mm pressure have been measured by the Rutherford alternating potential method for fields ranging from 0.5 to 46 volts/cm. The limiting mobilities for zero field are calculated to be, for H₂, 6,700 cm/sec per volt/cm and for He, 10,840 cm/sec per volt/cm.Energy loss of an electron on impact in H₂ and He.---K. T. Compton's theory of electronic mobilities is shown to fit the observed variation of mobility with field strength provided it be assumed that the fraction of its energy an electron loses on impact is, in H₂, 2.16, and in He, 8.6 times what it would be were the collisions elastic.Mean free path of electrons in H₂ and He.---From the limiting values of the mobilities at zero field it is calculated that the mean free path of electrons in thermal equilibrium with the gas is for H₂ at 1 mm pressure, 0.0408 cm, and for He at 1 mm pressure, 0.066 cm. These values are approximately half the kinetic theory values.