Ion—Molecule Reactions in Propane

Abstract

Ion—molecule reactions in propane were studied using mass- and energy-resolved ion beams in a tandem mass spectrometer. The sequence of elementary reactions which lead to C3H8+ and C3H7+ as stable ions was established. Through the use of deuterium-labeled reagents it was established that the parent ions undergo rapid charge-exchange reactions but that the resonance hydride transfer reaction is not observed within sensitivity limitations of the instrument (k<10−12 cm3/molecule·sec). The alkene ions C2H4+ and C3H6+ react with propane by H− and H2− transfer reactions and the relative importance of these modes of reaction depends strongly on ion—neutral relative kinetic energy. Interesting rearrangement processes observed for the relatively low-intensity primary ions C2H3+ and C3H3+ were also studied as a function of ion kinetic energy. In general, atom-transfer reactions are favored over more complex rearrangement processes as ion velocity is increased and, in certain cases, new reaction channels are opened by the conversion of translational energy into internal energy.