Detection opportunity for aromatic signature in Titan s aerosols in the 4.1 to 5.3 micron range

TL;DR

This study investigates how the inclusion of aromatic pyridine in laboratory simulations affects the infrared spectral signatures of Titan's aerosols, potentially explaining observations from Cassini's VIMS instrument.

Contribution

It demonstrates that aromatic compounds like pyridine significantly alter the infrared signature of Titan aerosol analogs, revealing new insights into aerosol composition.

Findings

Aromatic signatures appear in the 4.1-5.3 micron range when pyridine is included.

Spectral shifts in nitrile bands are observed with aromatic inclusion.

Results may explain Titan's aerosol spectral features observed by Cassini.

Abstract

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