High Pressure Photoionization Mass Spectrometry. III. Reactions of NO+(X 1Σ+) with C3–C7 Hydrocarbons at Thermal Kinetic Energies

The vapor phase reaction of NO+(X 1Σ+) with C3 through C6 normal, branched, or cyclic alkanes was found to proceed exclusively via an H− transfer mechanism, NO+(X 1Σ+)+RH2→RH++HCO. In addition to (I), C4H9+ was also formed by a second-order process in the reaction with 3-methylhexane. Absolute rate constants were determined for all systems at thermal kinetic energies. Isomers containing tertiary H atoms were found to be the most reactive, exhibiting rate constants on the order of 10+9 cm3/molecule·sec. Isotopic labeling has verified that the tertiary site is involved in the H− transfer reaction in those molecules having both secondary and tertiary H atoms. The rate constants found for n-alkanes and nonsubstituted cycloaklanes fall in the range 10−12–10−10 cm3/molecule·sec. The bimolecular reaction cyclo-C6H11++NO→C6H11NO+ was also noted at higher pressures. No further reaction of the RH+ species generated in (I) was found in any other RH2–NO combination at pressures up to 0.5 torr.