Interstellar carbonaceous dust and methane- water ice theoretical DFT structure and infrared spectroscopy

COST Action CM1401, Faro (Portugal), 16-20 Jan 2017. -- https://astrochem2017.sciencesconf.org/Solar system objects like outer planets, their satellites, comets and asteroids contain a carbonaceous structure often covered by ices of different composition. The carbonaceous content is assumed to be formed by hydrogenated amorphous carbon (HAC). The most abundant ices are made of H2O, CH4, CH3OH, NH3 and others. Our goal in this work is to make theoretical models using quantum chemical tools, like ab initio and DFT methods, for mixtures of ices with various compositions and predict their spectra, aiming to match the space observations. Were the theoretical models that are constructed to study these systems are shown. Systems that have been recently studied by our laboratory group also. Related to methane-water ice, the so-called breathing mode of methane due its tetrahedral structure, the C atom and the charge distribution remain undisturbed during the vibration, and no net dipole moment is generated. Thus, as is well known, this vibrational mode is inactive in the infrared spectrum. However, in low-temperature methane/water mixtures, like those generated to model astrophysical ices, a small but distinguishable feature has been observed in IR spectra, at the expected frequency of this vibration, Gálvez et al [1]. We will present in this communication our results for a number of quantum chemical models for methane/water mixtures with an explanation of this phenomenon [2] Fig.1. Two different models for the arrangements of a-C:H particles, Fig. 2, have been studied. Calculations with varying density values allow proposing structures with low density, in the range 0.75 to 1 g cm-3 as the most likely constituents of the experimental a-C:H samples named RC, (rings and chains ) model and SG (substituted graphite) model[3].Peer Reviewe