Ion-Molecule Reactions and Thermal Decomposition of Ions in N2-O2-Alkane (C2-C8) Mixtures Studied by Time-Resolved Atmospheric Pressure Ionization Mass

Article abstract of DOI:10.1021/j100316a025

The experiments were carried out at temperatures ranging from 236 to 569 K.The O2⁺ ion reacted with n-alkanes (CnH2n+2) via fast nondissociative and dissociative charge-transfer channels, its proportion depending on temperature.The nondissociative product CnH(2n+2)⁺ subsequently reacted with O2 via a slow H atom transfer path, producing alkyl ions.With increasing temperature the alkane ions CnH(2n+2)⁺ (n >/= 4) began to decompose thermally, producing olefinic ions and alkanes.The product olefinic ions CmH2m⁺ (m=4,5,6) reacted with O2 via a slow H atom transfer path, producing alkenyl ions CmH(2m-1)⁺.The C8H17⁺ decomposed thermally forming fragment alkyl ions and olefins.The fragment alkyl ions reacted with n-C8H18 reproducing C8H17⁺, thus leading to a chain mechanism in n-C8H18 decomposition.The equilibrium reaction, C2H5⁺ + C2H6 ->/<- C4H11⁺, and the subsequent dissociative rearrangement reaction, C4H11⁺ -> C4H9⁺ + H2, were studied.The reactions of NO⁺ and NOO⁺, both minor products of the irradiation of N2-O2 mixtures, with alkanes were also studied.The rate constants of the ion-molecule reactions and the unimolecular thermal decomposition reactions and the equilibrium constant were measured.