Metastable Ions Formed by Electron Impact in Hydrocarbon Gases

Abstract

It has been recently reported that the non-integral masses appearing in the mass spectra of various hydrocarbons may be explained by the spontaneous dissociation of some of the ions into fragments of lighter mass after they have been accelerated and emerge from the ion gun. By means of an energy filter, an energy analysis of the non-integral masses in n-butane, butadiene, and ethane has been made and the values obtained agree with those predicted on the basis that they arise from metastable ions. Variation of the pressure and electrode potentials confirms that the dissociation is spontaneous. The formation of metastable ions appears to be a general occurrence in the ionization and dissociation of hydrocarbons and is shown here to occur in ethane, propane, 1,3-butadiene, butene-1, cis-butene-2, isobutylene, normal butane, iso-butane, pentene-2, normal pentane, iso-pentane, and methyl-cyclo-pentane.