ABSOLUTE INTEGRAL CROSS SECTIONS FOR THE STATE-SELECTED ION-MOLECULE REACTION N-2(+)(X-2 Sigma(+)(g); v(+)=0-2) + C2H2 IN THE COLLISION ENERGY RANGE OF 0.03-10.00 eV

作者：Xu Yuntao; Xiong Bo; Chang Yih Chung; Ng C Y^*

来源：Astrophysical Journal, 2016, 827(1): 17.

DOI：10.3847/0004-637X/827/1/17

• astrochemistry
• methods: laboratory: molecular
• planets and satellites: atmospheres
• planets and satellites: individual (Saturn, Titan)

Using the vacuum ultraviolet laser pulsed field ionization-photoion source, together with the double-quadrupole-double-octopole mass spectrometer developed in our laboratory, we have investigated the state-selected ion-molecule reaction N-2(+)(X-2 Sigma(+)(g); v(+) = 0-2, N+ = 0-9) + C2H2, achieving high internal-state selectivity and high kinetic energy resolution for reactant N-2(+) ions. The charge transfer (CT) and hydrogen-atom transfer (HT) channels, which lead to the respective formation of product C2H2+ and N2H+ ions, are observed. The vibrationally selected absolute integral cross sections for the CT [sigma(CT)(v(+))] and HT [[sigma(HT)(v(+))] channels obtained in the center-of-mass collision energy (E-cm) range of 0.03-10.00 eV reveal opposite E-cm dependences. The sigma(CT)(v(+)) is found to increase as E-cm is decreased, and is consistent with. the long-range exothermic CT mechanism, whereas the E-cm enhancement observed for the sigma(HT)(v(+)) suggests effective coupling of kinetic energy to internal energy, enhancing the formation of N2H+. The sigma(HT)(v(+)) curve exhibits a step at E-cm = 0.70-1.00 eV, suggesting the involvement of the excited C2H2+ (A(2)Sigma(+)(g)) state in the HT reaction. Contrary to the strong E-cm dependences for sigma(CT)(v(+)) and sigma(HT)(v(+)), the effect of vibrational excitation of N-2(+) on both the CT and HT channels is marginal. The branching ratios and cross sections for the CT and HT channels determined in the present study are useful for modeling the atmospheric compositions of Saturn's largest moon, Titan. These cross sections and branching ratios are also valuable for benchmarking theoretical calculations on chemical dynamics of the titled reaction.

• 出版日期2016-8-10