Translational energy loss spectrometry of molecular dications from methane

Single electron loss processes have been studied in collisions of singly charged CH<SUP>+</SUP><SUB>n</SUB> ions (for n = 1-5) with Kr, CH<SUB>4</SUB>, N<SUB>2</SUB> and air at impact energies in the 0.5-5 keV range. By means of translational energy loss spectrometry of product molecular ions the double ionization energies of CH, CH<SUB>2</SUB>, CH<SUB>4</SUB> and CH<SUB>5</SUB> molecules have been deduced. No signal corresponding to CH<SUP>2+</SUP><SUB>3</SUB> could be detected. Comparison is made between the present results and data obtained by means of Auger spectroscopy, double charge transfer and charge stripping in a conventional mass spectrometer as well as with recent ab initio molecular orbital calculations. Agreement between experiment and theory as well as between different experiments is generally found to be unsatisfactory