The Ionization by Slow Electron Impact of Ammonia and Hydrogen Sulphide

Abstract

The molecules of ammonia and hydrogen sulphide have been studied by the usual method of positive-ray analysis, such as used by Dempster, Smyth, and others. In the case of ammonia, three principal types of ion at $\frac{m}{e}=15, 16, \mathrm{and} 17$ respectively, occurred. These are interpreted as having the compositions (N${\mathrm{H})}^{+}$, ${\left(\mathrm{N}{\mathrm{H}}_2\right)}^{+}$, and ${\left(\mathrm{N}{\mathrm{H}}_3\right)}^{+}$, with ionization potentials of 11.2±1.5 volts, 12.0±1.5 volts, and 11.2±1.5 volts, respectively. Since, with increasing pressure, the (N${\mathrm{H})}^{+}$ ion increases, the ${\left(\mathrm{N}{\mathrm{H}}_2\right)}^{+}$ ion remains sensibly constant, and the ${\left(\mathrm{N}{\mathrm{H}}_3\right)}^{+}$ ion decreases, it is concluded that the ${\left(\mathrm{N}{\mathrm{H}}_3\right)}^{+}$ and ${\left(\mathrm{N}{\mathrm{H}}_2\right)}^{+}$ ions result directly from the electron impact with the neutral N${\mathrm{H}}_3$ molecule, while the (N${\mathrm{H})}^{+}$ ion is probably produced by breakdown of the ${\left(\mathrm{N}{\mathrm{H}}_3\right)}^{+}$ ion by a reaction such as ${\left(\mathrm{N}{\mathrm{H}}_3\right)}^{+}$+N${\mathrm{H}}_3$=(N${\mathrm{H})}^{+}$+${\mathrm{H}}_2$+N${\mathrm{H}}_3$. For both ammonia and hydrogen sulphide, very few, if any, hydrogen ions and no negative ions were observed, tending to show that thermal dissociation was of little importance in affecting the results. For ammonia, very small peaks at $\frac{m}{e}=14\mathrm{} \mathrm{and} 18$ respectively, were observed. Their compositions are probably ${\mathrm{}\left(\mathrm{N}\right)\mathrm{}}^{+}$ and either ${\left(\mathrm{N}{\mathrm{H}}_4\right)}^{+}$ or ${\left({\mathrm{H}}_2\mathrm{O}\right)}^{+}$, and their origin is either secondary (from collision of ions with neutral molecules) or they result from impurities. In the case of hydrogen sulphide, three principal types of ion were likewise observed. They occur at $\frac{m}{e}=32, 33, \mathrm{and} 34$ and are interpreted as having the compositions ${\mathrm{}\left(\mathrm{S}\right)\mathrm{}}^{+}$, (H${\mathrm{S})}^{+}$, and ${\left({\mathrm{H}}_2\mathrm{S}\right)}^{+}$, respectively. Using Mackay's value of the lowest ionization potential as a standard for the calibration of the voltage scale, the ionization potentials are approximately 10.4 volts, 16.9 volts, and 15.8 volts, respectively. Variation of the pressure, at low pressures, indicates that no secondary processes occur, i.e. that the ions above named are all formed by the initial process of the electrons colliding with the gas molecules. No ${\mathrm{S}}_2^{+}$ ions were observed, nor any which could be due to isotopes of sulphur.