Trochoidal Electron Impact Time-of-Flight Mass Spectrometry of Chlorodifluoromethane

A Time-of-Fight mass spectrometer (TOF-MS) equipped with both a standard electron gun and a trochoidal electron monochromator was constructed and made operational and used to study ionization processes of the molecule Chlorodifluoromethane (CHF₂Cl). The appearance energies of both the parent ion (CHF₂Cl⁺) and the most intense fragment ion (CHF₂⁺) were carefully analyzed and it was observed that the energy for formation of the parent ion, (CHF₂Cl⁺) at 12.50 eV, was at a higher energy than the fragment ion, (CHF₂⁺) at 12.25 eV. This phenomenon has to our knowledge never before been reported in the literature and is of great interest. The trochoidal electron monochromator allowed for the energy distribution of the ionizing electron beam to be within the difference of the appearance energies for the ions, confirming the result. Metastable decay analysis of the parent ion showed two parent ion states present. One state decayed with a lifetime of 2 ms and another parent ion state appeared to be stable. It was also shown that the parent ion readily dissociated into the CHF₂⁺ fragment ion and possible mechanisms for this effect is discussed. The results show the need for future theoretical calculations of the ionic potential energy surfaces for this molecular cation in order to assess the various possibilities for this mechanism. The atmospheric relevance of the instability of the parent ion of CHF₂Cl and its short lifetime to dissociation, in which an ozone destroying chlorine atom is released, should be further considered.