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L. J. Stief, R. P. Thorn, F. L. Nesbitt (NASA/Goddard Space Flight Center), S.-C. Kuo, R. B. Klemm (Brookhaven National Laboratory)
To account for the present atmosphere of Titan, scenarios considered include the photodissociation or the shock heating of primordial NH3 to yield N2. During the conversion from an NH3 to an N2 atmosphere in these scenarios, both NH2 and N will be present. The interaction of these species via the rapid N + NH2 reaction has not been considered to date. Two previous laboratory studies were interpreted in terms of the process: N + NH2 arrow N2 + 2H. In direct discharge flow-photoionization mass spectrometry (DF-PIMS) experiments at the National Synchrotron Light Source (NSLS), we have detected the N2H2 molecule as a product of the N + NH2 reaction based on a measurement of the known PIMS spectrum and threshold for N2H2. This suggests the additional reaction channel: N + NH2 arrow N2H2. In the primodial atmosphere of Titan, N2H2 may futher react or perhaps thermally decompose, in either case leading to N2 formation. In the present atmosphere of Titan, reaction of N with hydrocarbon free radicals leads to formation of products containing the CN bond. We measured the PIMS spectra and thresholds for the products of the N + C2H3 reaction in DF-PIMS experiments at the NSLS. We observed that the C2H3N adduct species formed was exclusively the lowest energy isomer CH3CN. However, the major product, the C2H2N free radical, was shown not to be the lowest energy isomer CH2CN. There are five known C2H2N isomers and identification of the isomer or isomers formed in the N + C2H3 reaction requires additional information on the PIMS spectrum and threshold for each of the remaining four isomers. Although CH3CN has been observed in the atmosphere of Titan, the reaction N + C2H3 arrow CH3CN is not the only potential source of this molecule.