Ab initio calculations of Raman and IR spectra of orthoenstatite and forsterite: lattice dynamics and modelling for planetary remote sensing

Several spectroscopic techniques are capable of measuring the fundamental vibrational modes of minerals. The present study focuses on two spectroscopic techniques: Raman spectroscopy and emission spectroscopy, applied to the investigation of two well know mineral families olivine and orthopyroxenes. The motivations and applications of TIR spectral studies, and especially of these two minerals, are wide-ranging, covering fields from astronomy to mantle geophysics; in fact a wide variety of measurement techniques and samples analysis already exist in literature. However, in this study we present some innovations towards the approach applied on the subject: the calculation and the modelling of Raman and emission spectra at room ad at high temperature of those minerals with ab initio quantum mechanics calculations. The approach is carried out employing hybrid HF/DFT approach for its accuracy and reliability calculating vibrational frequencies by means of the computer code CRYSTAL14, which enable a reliable simulation of a full vibrational pattern. Two different kinds of case studies will be shown, one focused on Raman spectroscopy and the other one concerning the modelling of emissivity spectra at high temperature, both cases aim to verify the reliably of this simulation and if it can foresee the trend of spectral features due to temperature. The investigation is mostly focused on the possibility to develop an application of the method on the data that will be acquired by MERTIS, the Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) on board of the ESA BepiColombo Mercury Planetary Orbiter spacecraft due in 2018.