The Ionization of HCI by Electron Impacts

Ionization of HCl.---Current-voltage curves obtained by means of a two electrode, hot cathode discharge tube indicate ionization in stagnant HCl gas at 14 volts in agreement with the value of the ionizing potential reported by previous observers. Spectrograms showed no hydrogen lines at voltages near the ionizing potential, but they appeared faintly at higher voltages along with some bands. A considerable amount of dissociation of the gas was observed, and this was shown to be due to thermal action at the filament rather than to the discharge. The presence of dissociation products made the interpretation of the critical potential doubtful, and so the apparatus was modified to eliminate these from the region of observation. With HCl flowing continuously through a three element discharge tube in such a way that it passed through the observation chamber, where the electron impacts occurred, before it reached the filament, no hydrogen lines appeared at accelerating voltages up to 120 volts. Current-voltage curves again show a critical potential at 14 volts which is attributed to the ionization of the molecule without dissociation. No band spectra of wave-lengths between 6000 and 2000A accompany this excitation. Hence it is concluded that the molecule has no electron transitions involving a change of energy between 2 and 6 volts. When an HCl⁺ ion is neutralized, the electron is probably bound in a single operation with the consequent radiation of energy equivalent to about 14 volts.Effect of HCl on a tungsten filament.---The conductivity was observed to increase 10 percent in 5 hr. Langmuir suggests that WCl₆ formed at the cooler ends is dissociated at the hot section.