  Chemistry in Titan's N2-CH4 atmosphere produces complex organic aerosols. The
chemical processes and the resulting organic compounds are still far from
understood, although extensive observations, laboratory, and theoretical
simulations have greatly improved physical and chemical constraints on Titan's
atmosphere. Here, we conduct a series of Titan atmosphere simulation
experiments with N2-CH4 gas mixtures and investigate the effect of initial CH4
ratio, pressure, and flow rate on the production rates and composition of the
gas and solid products at a Titan relevant temperature (100 K) for the first
time. We find that the production rate of the gas and solid products increases
with increasing CH4 ratio. The nitrogen-containing species have much higher
yield than hydrocarbons in the gas products, and the N-to-C ratio of the solid
products appears to be the highest compared to previous plasma simulations with
the same CH4 ratio. The greater degree of nitrogen incorporation in the low
temperature simulation experiments suggests temperature may play an important
role in nitrogen incorporation in Titan's cold atmosphere. We also find that H2
is the dominant gas product and serves as an indicator of the production rate
of new organic molecules in the experiment, and that CH2NH may greatly
contribute to the incorporation of both carbon and nitrogen into the solid
particles. The pressure and flow rate affect the amount of time of the gas
mixture exposed to the energy source and therefore impact the N2-CH4 chemistry
initiated by the plasma discharge, emphasizing the influence of the energy flux
in Titan atmospheric chemistry.
