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

Abstract

The vapor phase reaction of ${\mathrm{NO}}^{+}{\mathrm{(X}}^1{\Sigma }^{+})$ with C₃ through C₆ normal, branched, or cyclic alkanes was found to proceed exclusively via an H⁻ transfer mechanism, $${\mathrm{NO}}^{+}{\mathrm{(X}}^1{\Sigma }^{+}\mathrm{)+}{\mathrm{RH}}_2\to {\mathrm{RH}}^{+}+\mathrm{HCO}.$$ 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.