Quantum-State-Selected Integral Cross Sections and Branching Ratios for the Ion-Molecule Reaction of N2+(X2Σg+: ν+=0-2) + C2H4 in the Collision Energy Range of 0.05-10.00 eV

By implementing a vacuum ultraviolet laser-pulsed field ionization-photoion ion source with a double quadrupole-double octopole ion guide mass filter, we have obtained detailed quantum-vibrational-state-selected integral cross sections a, nu(+) = 0-2, for the ion-molecule reaction of N-2(+)(X-2 Sigma(+)(g): nu(+) = 0-2) + C2H4 in the center-of-mass kinetic energy range of E-cm = 0.05-10.00 eV. Three primary product channels corresponding to the formation of C2H3+, C2H2+, and N2H+ ions are identified with their sigma(nu+) values in the order of sigma(nu+)(C2H3+) > sigma(nu+)(C2H2+) > sigma(nu+)(N2H+). The minor sigma(nu+)(N2H+) channel is strongly inhibited by E-cm and observed only at E-cm < 0.70 eV. The high sigma(nu+)(C2H3+) and sigma(nu+)(C2H2+) values indicate that C2H3+ and C2H2+ product ions are formed by prompt dissociation of internally excited C2H4+ (C2H4+*) intermediates produced via the near-energy-resonance charge-transfer mechanism. The sigma(nu+)(C2H3+) and sigma(nu+)(C2H2+) are found to drop only mildly or stay nearly constant as a function of E-cm in the range of 0.05-6.00 eV. This observation is contrary to the expectation of a steep decline for the sigma(nu+) value commonly observed for an exothermic reaction pathway as E-cm is increased. Significant vibrational enhancement is observed for the sigma(nu+)(C2H3+) and sigma(nu+)(C2H2+) at nu(+) = 2 and in the E-cm range of similar to 0.20-7.00 eV. The branching ratios sigma(nu+)(C2H3+):sigma(nu+)(C2H2+):sigma(nu+)(N2H+) are also determined with high precision by measuring the intensities of product C2H3+, C2H2+, and N2H+ ions simultaneously at fixed E-cm values. The sigma(nu+) and branching ratio values reported here are useful contributions to the database needed for realistic modeling of the chemical compositions and evolutions of planetary atmospheres, such as the ionosphere of Titian. The quantum-state-selective results can also serve as experimental benchmarks for theoretical calculations on fundamental chemical reaction dynamics.