Dissociation of Hydrogen and Nitrogen by Excited Mercury Atoms

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 theH₂ molecules receive energy for dissociation from excited Hg atoms in the 2p₂ state.Dissociation of nitrogen in low-voltage arcs.---Similar experiments with nitrogen, using pure Mg metal to absorb the dissociated nitrogen, showed a dissociating effect of excited mercury atoms, but only about one tenth as large as the effect in H₂. Reasons are given for believing that in N₂ the dissociation is produced by Hg atoms in the $2P$ state. This conclusion is supported by results obtained by others on the disappearance due to phosphorus vapor, but is apparently at variance with the similar effect of arsenic vapor. Clean-up due to electron impacts, 17 to 100 volts, is small to 25 volts, increases four fold to 70 volts, and 10 fold for voltages above 70. The effect is related to the intensity of the line spectrum. Above 70 volts, a very active form of nitrogen is produced, resulting in a "flare."