Photochemistry of HCN Ice on Tholins Simulated in Titan’s Lower Atmosphere Conditions

International audienceTitan’s organic atmospheric chemistry is unique in the Solar System. Revealed by the Voyager and ongoing Cassini Missions, a variety of latitudinal and altitudinal-changing trace species broken down from the initial N2-CH4 (98-2%) composition, are found in Titan’s atmosphere in the gas phase and as ices (e.g. C4N2, HCN) above the poles. Hydrogen cyanide (HCN) is the most common nitrile trace volatile and is known to reach condensation point at stratospheric altitudes. Furthermore, high energy irradiation in the upper atmosphere (~1400km) initiates gas phase reactions known to produce the thick aerosol layers. These aerosols precipitate down to the surface while interacting with the gas medium and are subject to potential condensation of trace species such as HCN onto their surface. The reactivity of HCN is still quite unknown and its potential for prebiotic chemistry pertains to Titan conditions. Thus, we investigate whether the irradiation reaching Titan’s lower atmosphere and near-surface conditions be reactive enough to induce photochemicalreactions of condensed HCN ice. To do tackle question, we turn to laboratory simulations of HCN ice deposits on tholins irradiated at wavelengths relevant to low-altitude and near-surface conditions. Ice analysis is performed with in situ Fourier-Transform Infrared and UV-VIS spectroscopy