Phenomena in Gases Excited by Radio Frequency Currents

Undamped Radio Frequency Vacuum Discharges through Hydrogen, Oxygen and Air.—(1) The spectra, 5000-3500 Å., were found to be the same for frequencies of 3 × ${10}^5$ to 4 × ${10}^6$ as for 60 cycles, with currents of the same strength. (2) The minimum discharge potentials for electrode distances from 5 to 30 mm. and pressures of from 1 to 5 mm. of mercury were also found to be independent of the frequency and the same as for direct currents. A theoretical discussion of this result leads to the conclusion that the discharge is initiated by collisions of electrons, rather than of gaseous ions, with gas molecules. (3) Persistence of each discharge was studied with the aid of a mirror rotating 200 times per second. Damped discharges with a frequency of ${10}^6$ cycles or less showed separate flashes but those with higher frequencies were blended together. This difference may perhaps be due to the limitations of the apparatus used. With damped oscillations the color of the discharge changed with the voltage as would be expected.