The Heats of Dissociation of Hydrogen and Nitrogen

Abstract

A method previously described has been employed to determine the heats of dissociation of the normal molecule and the molecular ion for ${\mathrm{H}}_2$ and ${\mathrm{N}}_2$. A new apparatus has been constructed of tantalum, which eliminates previous difficulties, believed due to contact potentials. As previously shown, electrons passing through diatomic gases are able to produce atomic ions possessing kinetic energies of several volts. Simultaneous measurements of the electron energy necessary to produce atomic ions and the kinetic energy of the ions permit the determination of the heats of dissociation. The values obtained are $D\left({{\mathrm{H}}_2}^{+}\right)=2.59\mathrm{}\pm 0.03$ v, $D\left({\mathrm{H}}_2\right)=4.43\mathrm{}\pm 0.03$ v, $D\left({{\mathrm{N}}_2}^{+}\right)=6.73\mathrm{}\pm 0.02$ v, $D\left({\mathrm{N}}_2\right)=7.90\mathrm{}\pm 0.02$ v. It is concluded that these results are free from systematic errors to ±0.1 v. A critical comparison of these data is made with the results of other methods, mainly spectroscopic.