Dissociation of Hydrogen and Nitrogen by Excited Mercury Atoms

Abstract

Dissociation of hydrogen in low-voltage arcs.—Arcs were maintained from a heated Mo filament to a Ni anode and the rate of dissociation was measured by the change of pressure produced as a result of oxidation of the atomic hydrogen by nearby copper oxide and of freezing out of the resulting water vapor. In pure hydrogen there is no dissociation, other than that due to the hot cathode, below a minimum voltage (13), but above the minimum arcing voltage (16) the rate was rather rapid, decreasing somewhat with increasing voltage to 65, the highest tried. In mercury arcs, however, the dissociation was at least 10 times more rapid in the 5 volt arc and 3 times more rapid in the 10 volt arc. This rapid dissociation is attributed to collisions of the "second kind" whereby the${\mathrm{H}}_2$ molecules receive energy for dissociation from excited Hg atoms in the $2p_2$ state.