  The Cassini/Huygens mission provided new insights on the chemistry of the
upper atmosphere of Titan. The presence of large molecules and ions (>100 s of
amu) detected by Cassini at high altitude was not expected, and questions the
original assumptions regarding the aerosol formation pathways. From recent
laboratory studies, it has been shown that the inclusion of trace amounts of
aromatic species drastically impacts the chemistry of aerosol formation and
induces observable changes in the properties of the aerosols. In the present
work we focus on the effect of one of the simplest nitrogenous aromatics,
pyridine (C5H5N), on the infrared signature of Titan s aerosol analogs. We
introduce initial gas mixtures of: (i) N2-C5H5N (100%/250ppm), (ii)
N2-CH4-C5H5N (99%/1%/250ppm), (iii) N2-CH4 (99%/1%) in a cold plasma discharge.
The material produced, herein called tholins, is then analyzed by mid-infrared
spectroscopy. When adding pyridine in the discharge, the tholins produced
present an aromatic signature in the 4.1-5.3 micron (1850-2450 cm-1) spectral
region, attributed to overtones of aromatic C-H out-of-plane bending
vibrations. We also observe a spectral shift of the nitrile and iso-nitrile
absorption band with the inclusion of pyridine in the gas mixture. These
results could help to investigate the data obtained at Titan by the
Cassini/VIMS instrument in the 1-5 micron infrared window
