Mid- and far-infrared absorption spectroscopy of Titan's aerosols analogues

In this work we present mid- and far-infrared absorption spectra of Titan's aerosol analogues produced in the PAMPRE experimental setup. The evolution of the linear absorption coefficient epsilon (cm(-1)) is given as a function of the wavenumber. We provide a complete dataset regarding the influence that the concentration of methane vapor in the gas mixture has on the tholin spectra. Among other effects, the intensity of the 2900 cm(-1) (3.4 mu m) pattern (attributed to methyl stretching modes) increases when the methane concentration increases. More generally, tholins produced with low methane concentrations seem to be more amine based polymers, whereas tholins produced with higher methane concentrations contains more aliphatic carbon based structures. Moreover, it is shown that the position of the bands around 2900 cm(-1) depends on the chemical environment of the methyl functional group. We conclude that the presence of these absorption bands in Titan's atmosphere, as measured with the VIMS instrument onboard Cassini is in agreement with an aerosol contribution. We also compare the far-infrared spectrum of tholin to spectra of Titan's aerosols derived from recent Cassini-CIRS observations displaying many similarities, particularly with absorption bands at 325 cm(-1), 515 cm(-1), and the methyl attributed 1380 cm(-1) and 1450 cm(-1) bands. (C) 2012 Elsevier Inc. All rights reserved.