Reactions of selected molecular anions with oxygen

An investigation of the gas‐phase reactions of molecular oxygen with the molecular anions of 17 compounds formed by resonance electron capture was undertaken using a pulsed e‐beam high‐pressure mass spectrometer. The molecular anions of sulphur hexafluoride, perfluromethylcyclohexane, cis‐ and trans‐perfluorodecalin, m‐chloronitrobenzene, o‐, m‐and p‐fluoronitrobenzene and o‐, m‐ and p‐dinitrobenzene were found to be unreactive towards oxygen. Those of o‐ and p‐chloronitrobenzene, penta‐ and perchlorobenzene, perfluorobenzene, and perfluorotoluene were found to react readily with oxygen. The second‐order rate constants for these reactions are shown to bear an inverse dependence on temperature. The reactions involving o‐ and p‐chloronitrobenezene and penta‐and perchlorobenzene proceed via a branched mechanism by which an ion of the type [M + O − Cl]− and Cl− ion are simultaneously produced. A greater variety of negative ions are formed in the reactions of the molecular anions of perfluorobenzene and perfluorotoluene with oxygen. The electron affinities of pentachlorobenzene (0.7 eV) and perchlorobenzene (1.0 eV) are also reported for the first time.