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Using a Nier-type electron impact ion source in combination with a double focusing two sector field mass spectrometer, partial cross sections for electron impact ionization of acetylene are measured for electron energies up to 1000 eV. Discrimination factors for ions are determined using the deflection field method in combination with a three-dimensional ion trajectory simulation of ions produced in the ion source. Analysis of the ion yield curves obtained by scanning the deflectors allows the assignment of ions with the same mass-to-charge ratio to specific production channels on the basis of their different kinetic energy distributions. This analysis also allows to determine, besides kinetic energy distributions of fragment ions, partial cross sections differential in kinetic energy. Moreover a charge separation reaction, the Coulomb explosion of the doubly charged parent ions C2H2++ into the fragment ions C2H+ and H+, is investigated and its mean kinetic energy release (=3.88 eV) is deduced. [ABSTRACT FROM AUTHOR]

Abstract: Doubly charged ions produced by electron impact ionization of toluene (C7H8) show metastable unimolecular dissociation into two singly charged fragments. A high-resolution double focusing mass spectrometer (reversed Nier–Johnson type BE geometry) was used to monitor these decomposition reactions. We have identified four competing charge separation channels. The mass-analyzed ion kinetic energy (MIKE) technique was used to determine mean values of the kinetic energy release (KER). We obtained values of the average KER for the charge separation reactions of ranging from 2.5 to 3.5eV. [Copyright &y& Elsevier]

Abstract: Metastable ions C3HnN+ (n =1, 2 or 3) and C2H2 + produced by electron impact on the neutral C3H3N (acrylonitrile) undergo metastable decay reactions resulting in the fragment ions C3HmN+ (m =1, 2) or C2H2 +. We have monitored these reactions in a double focusing mass spectrometer of reversed B-E geometry. To identify the fragment ions and determine their kinetic energy release distribution (KERD), the mass-analyzed ion kinetic energy (MIKE) scan technique was utilized. For the above mentioned ions we obtained average KER values ranging from 9 up to 23meV. Moreover, the fractions of decaying ions were measured. We have found the existence of two states of the metastable C2H2 + ion, one with a short life time of about 0.27μs and the other one which is most likely a completely stable ion state. [Copyright &y& Elsevier]