The Spectra of Mercury Above the Ionization Potential

Abstract

Excitation of arc spectra of Hg by electrons having velocities above the ionization potential. Effect of recombination.---Electrons in mercury vapor with velocities greater than the ionization potential were confined into a beam by a magnetic field. The light produced was projected on the slit of a spectroscope with the direction of the beam at right angles to the slit. Perpendicular to the beam an electric field withdrew positive ions before they recombined. The intensity of the arc lines was found to be independent of the electric field which indicates that recombination contributes very little to the formation of these lines. These results are contrary to the previously accepted explanation given for the complete arc spectrum appearing above the ionization potential. Consequently in addition to simple excitation the arc spectrum can be explained in the two following ways, (1) as being due to the return to the $1^{1}S_{0}$ state by an electron which has been displaced from an inner energy level to a virtual orbit while simultaneously one of the electrons of the valency group falls in to fill the vacated level; (2) due to a special type of recombination which is called initial recombination.Intensity variation of the spark lines due to the motion of the positive ions.---Spark lines due to singly and doubly charged ions show a variation of intensity along their length in such a manner that it is possible to distinguish them from the arc lines. It is also possible to differentiate between the lines of the first and the second spark spectrum.