Probability and Critical Potentials for the Formation of Multiply Charged Ions in Hg Vapor by Electron Impact

Abstract

With a type of apparatus previously reported the procedure is described for measuring the probability of the formation of multiply charged ions in mercury vapor as a function of the velocity of the incident electron.Critical potentials for the formation of multiply charged ions. New results together with those of an earlier paper place the minimum or ionizing potentials for the formation of ${\mathrm{Hg}}^{+}$, ${\mathrm{Hg}}^{2+}$, ${\mathrm{Hg}}^{3+}$, ${\mathrm{H}}^{4+}$, and ${\mathrm{Hg}}^{5+}$ by a single impact at 10.4, 30, 71, 143, and 225 volts respectively. A brief correlation of these results with those of other observers is given.Relative numbers of multiply charged ions. A set of curves is given showing the fraction of the total positive ion current carried by each type of ion as a function of the electron velocity. Another set of curves shows the fraction of the total number of ions carrying one, two, three, four, and five charges. The fraction for ${\mathrm{Hg}}^{+}$ drops to a nearly constant value of 78 percent while the value for ${\mathrm{Hg}}^{2+}$ approaches 16 percent of the total number beyond 150 volts. At 400 volts the values for the five ions in order are 77, 16.5, 4.4, 1.3 and 0.8 percent respectively.Quantitative measure of the number of ions produced and effective cross-sectional area of the Hg atom. Curves are given representing the number, $N$, of each type of ion, per electron, per cm path, per mm pressure at 0\ifmmode^\circ\else\textdegree\fi{}C as a function of the electron velocity. The values of $N$ for ${\mathrm{Hg}}^{+}$, ${\mathrm{Hg}}^{2+}$, ${\mathrm{Hg}}^{3+}$, and ${\mathrm{Hg}}^{4+}$ have maxima of 20.8, 3.2, 0.72, 0.15 at 50, 115, 210, and 400 volts respectively. The effective cross-sectional area of the Hg atom toward an ionizing collision of a given type is obtained by dividing the appropriate value of $N$ by the number of molecules per cc. The maximum value of this area for ${\mathrm{Hg}}^{+}$ is about 60 percent of the kinetic theory value.A discussion is given of the meaning of the area under the peaks in the $\frac{e}{m}$ analysis curves and its effect on the accuracy of the interpretation of the data.