Covariance mapping mass spectroscopy using a pulsed electron ionizing source: application to CF4

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Abstract
We report the implementation of covariance mapping mass spectroscopy to pulsed-electron-beam ionization time-of-flight mass spectroscopy. The technique has been applied to CF4 and evidence is presented for the previously unreported doubly coincident ionization channels: CF2++F2+, CF++F2+, CF2+F+, F2++F+, C++F2++F2+F+, C2++F+, and F++F+ at electron impact energies of 100, 200, 300, 400 and 500 eV. In addition, indications for an unstable CF4+: parent ion are presented. Furthermore, sufficient statistics were accumulated to allow an attempt to determine the momentum distribution for the ions in several previously reported double ion channels (CF3+F+, CF2+F++, CF++F+, and C++F+) using a Monte Carlo method. Evidence for translational kinetic energies in excess of 10 eV was observed for some of the lighter ions. The magnitude of the resultant momentum from unobserved neutral fragments and the angle between the two detected ion momenta were calculated as well. The experiment was aided by the development of a fast data collection system. Contour maps of the major covariance mapping peaks were obtained with a time resolution of16 ns at an experimental repetition rate of 50 kHz over a time-of-flight range of 8 mu s.