Ionization Potentials of Perfluorocycloalkanes

Abstract

THE peaks in the mass spectra of aliphatic saturated fluorocarbons corresponding to the molecule-ions have been described as vanishingly small¹. Under normal conditions of electron bombardment, less than 0.1 per cent of the total ion current is due to the molecule-ion so that determinations of the ionization potentials of these compounds by the electron impact method is not possible. It was shown recently in a mass spectrometric examination of cyclic fluorocarbons² that the molecule-ions of the perfluorocycloalkanes were at least ten times as abundant as those of the corresponding perfluoroalkanes, and it has thus been found possible by working at high pressures in the ion source (1 × 10⁻⁵ mm.) to determine the ionization potentials of perfluorocyclopentane and perfluorocyclohexane. The precision of the determination of the ionization potential of an ion of low abundance is less than that which is normally claimed for the electron impact method and is probably of the order of ±0.3 eV.