Triatomic Hydrogen as an Emitter of the Secondary Spectrum

It appears quite probable that some lines in the secondary spectrum of hydrogen may be emitted by an excited H'₃ molecule formed by the process H'₂+H₂{→}H'₃+H. Thus Richardson thinks that the question of the rival claims of H₂ and H₃ to his Hα, Hβ, Hγ, bands is unsettled. Allen and Sandeman have found a band system which they definitely ascribe to H₃. An attempt was made to verify these results by correlating the variation in the concentration of H₃⁺ ions and presumably of H₃ excited molecules with the variation in intensity of the lines.Variation with pressure of the concentration of H₃⁺ ions in the positive column of a glow discharge.---The concentration of H₃⁺ ions in the positive column of a glow discharge is found to decrease rapidly with pressure and becomes negligible at 0.01 mm. Reasons are given for believing that the recorded concentration of ions is even more truly representative of the conditions in a hydrogen discharge than the results given by the Lenard tubes of Smyth or of Hogness and Lunn.Effect of pressure on the relative intensities of the lines of the hydrogen secondary spectrum.---The relative concentration of H₃⁺ has no effect on the intensity of the lines of the secondary spectrum with the possible exception of some weak lines such as those of the Allen and Sandeman bands. Evidence is found from Lowe's curves which indicates that the Fulcher lines of Richardson's bands are emitted by the H₂ molecule.