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 σν+, ν+ = 0-2, for the ion-molecule reaction of N2+(X2Σg+: ν+ = 0-2) + C2H4 in the center-of-mass kinetic energy range of Ecm = 0.05-10.00 eV. Three primary product channels corresponding to the formation of C2H3+, C2H2+, and N2H+ ions are identified with their σν+ values in the order of σν+(C2H3+) > σν+(C2H2+) > σν+(N2H+). The minor σν+(N2H+) channel is strongly inhibited by Ecm and observed only at Ecm < 0.70 eV. The high σν+(C2H3+) and σν+(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 σν+(C2H3+) and σν+(C2H2+) are found to drop only mildly or stay nearly constant as a function of Ecm in the range of 0.05-6.00 eV. This observation is contrary to the expectation of a steep decline for the σν+ value commonly observed for an exothermic reaction pathway as Ecm is increased. Significant vibrational enhancement is observed for the σν+(C2H3+) and σν+(C2H2+) at ν+ = 2 and in the Ecm range of ∼0.20-7.00 eV. The branching ratios σν+(C2H3+):σν+(C2H2+):σν+(N2H+) are also determined with high precision by measuring the intensities of product C2H3+, C2H2+, and N2H+ ions simultaneously at fixed Ecm values. The σν+ 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.