Theoretical models for ice mixtures in outer solar system bodies

San Francisco, 12-16 December, 2016 ; http://fallmeeting.agu.org/2016/In a recent work [1], we have measured the optical constants and band strengths of methane/ethane ice mixtures in the near- and mid-infrared ranges. We present here recent calculations on models for these and other ice mixtures containing water. Methane and ethane are constituents of planetary ices in our solar system. Methane has been detected in outer solar system bodies like Titan, Pluto, Charon, Triton, or other TNO¿s [2]. Ethane has also been identified in some of those objects [2]. The motivation of this work has been to provide new laboratory data and theoretical models that may contribute to the understanding of those systems, in the new era of TNO¿s knowledge opened up by the New Horizons mission [3,4]. The models are designed to cover a range of mixtures of molecular species that match the composition and density of some of the systems in outer solar systems bodies. The calculations include several steps: first, amorphous samples are generated, via a Metropolis Montecarlo procedure (see Figure, left); next, the amorphous structures are relaxed to reach a minimum in the potential energy surface; at this point, the harmonic vibrational spectrum is predicted. Finally, the relaxed structures are processed by ab initio molecular dynamics simulations with the final aim of obtaining an anharmonic prediction of the spectra, which includes the near-infrared region (see Figure, right). Both the harmonic and anharmonic spectra are compared to experimental measurements in the mid- and near-infrared regions. All calculations are carried out by means of Materials Studio software [5], using the Density Functional Theory method, with GGA-PBE functionals and Grimme D2 dispersion correction.Peer Reviewe