Polycrystalline materials - comparison between theory and experiment

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The subject of this project will be the investigation of different theories (e.g. EMA, ARTT and ARIT) that all describe the (IR) reflection or transmission spectra of polycrystalline materials, and the ranges of applicability in detail. Some theories are only valid for large or small crystallites, isolated particles or compact samples, with or without taking into account the particle shape. We found, also with own investigations, that the results gained from the calculated spectra are not consistent with each other.The astronomer's interest in this situation is also very high since the information gained from the fitted spectra about particle size and shape determine the formation process of those particles. Therefore it is very important to gain information out of the measured spectra as precise as possible.Due to the lack of suitable samples with defined particle shape, size and distance to each other is it our intention to create "experimental" reference spectra with Finite Difference Time Domain calculations and compare spectra calculated with different theories to these spectra. The different theories also differ very strongly in the necessary calculation time and effort. We also intend to investigate the band splitting in dependency of the particle shape, which is predicted by one of the theories.With samples, that are produced in a clean room can we also investigate particle size effects and the band splitting for simple materials to a certain extend.It is e.g. necessary to determine the limits between "large" and "small" particles, "isolated" and "not so isolated" particles. The limits depend on the oscillator strengths of the corresponding transition dipole moment.With the so gained knowledge plan we to reproduce real measured, that means not by Finite Difference Time Domaine calculated spectra of aerosol measurements. The aerosol measurements are already performed and will be provided by the Institute of Astronomy.