Detection Opportunity for Aromatic Signature in Titan’s Aerosols in the 4.1–5.3 μm Range

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 (C 5 H 5 N), on the infrared signature of Titan's aerosol analogs. We introduce initial gas mixtures of: (i) N 2 -C 5 H 5 N (100%/250ppm), (ii) N 2 -CH 4 -C 5 H 5 N (99%/1%/250ppm), (iii) N 2 -CH 4 (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 µm (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 µm infrared window.

Photoprocessing of cationic triazacoronene: dissociation characteristics of polycyclic aromatic nitrogen heterocycles in interstellar environments

“…Nitrogen containing polyynes like HC n N, C n N, and NC n N chains have already been detected in the atmosphere of Titan as well as in the coma of the comet 67P/Churyumov-Gerasimenko. [47][48][49] They are also suggested to be abundant in interstellar objects, 50,51 but the absence of a dipole moment makes it hard to identify dicyanopolyynes. Recently M. Agu ´ndez et al 52 proposed the presence of NC 4 N in the dark molecular cloud TMC-1, based on the detection of its protonated derivative This journal is © the Owner Societies 2024 NC 4 NH + , providing first observational prove of their existence in the ISM.…”