Low Voltage Arcs in Iodine

Ionizing and radiating potentials in molecular and atomic iodine vapor.---Low voltage arcs in monatomic and molecular iodine vapor were investigated together with their spectra. From a study of the current-voltage curves it was concluded that 6.5 volts is the minimum radiating potential of the atom, 8.0 the ionizing potential of the atom, and 9.5 the ionizing potential of the molecule. Non-oscillating abnormal low voltage arcs were maintained down to 4.9 volts and oscillations were observed around 12 volts. With arc currents of about 2 amperes the filament current could be cut off and the arc sustained indefinitely at 30 volts or above.Variation with potential of spectra of molecular and atomic iodine.---At 4.9 volts the spectrum contained only three lines, (λλ2062, 2535, 3135), the continuous band 3460, and several groups of bands. At slightly higher voltages arc lines appear and at 8 volts the strongest spark lines begin. These lines are succeeded by new ones at higher voltages, making it probable that the stripping of the atom is in progress. Peculiar behavior of the lines 2535 and 3135A was observed. Three continuous bands (at 4080, 4300 and 4800A) are present in molecular but disappear in atomic iodine. A band system lying between 2224 and 2050A was observed and two groups of four bands each were found at 2880, 2833, 2776, 2716A and 2480, 2379, 2290 and 2243A.