Abstract:
A technique for mass-spectrometric investigation of the yield of positive ions produced by direct and electron-impact dissociative ionization of methane molecules is described, and respective experimental data are presented. Doubly charged Ñ$_2^+$, ÑÍ$_3^{2+}$, and ÑÍ$_4^{2+}$ ions, as well as singly charged D$_2^+$, ÑD$_3^+$, and ÑD$_4^+$ ions, are detected in the mass spectrum of a methane molecule at electron energy $U_e$ = 90 eV for the first time. From ionization efficiency curves, the ionization energy of the parent molecule and the appearance energy of fragment ions are determined. The ionization energy of the CH$_4$ molecule is found to be 12.62 $\pm$ 0.20 eV. Electron-molecular reactions that may take place when a low-energy electron beam interacts with a methane molecule are analyzed. The ionization process and the formation of methane molecule fragments are studied.
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