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UBC Theses and Dissertations

Computer simulation of infrared spectra and structures of molecular nanoparticles Firanescu, George


Molecular nanoparticles, i.e. molecular aggregates held together by weak intermolecular interactions, are ubiquitous in planetary atmospheres and the interstellar space. Although they play a crucial role for radiative energy transfer and chemical processes, the understanding of their properties — which can differ significantly from those of the bulk — is still in its infancy. The present thesis is devoted to a better understanding of the influence of intrinsic properties of these particles on their infrared spectra. The influence of shape, size, architecture and phase on infrared spectra is modeled at a molecular level and propensity rules are established. The high complexity of these huge aggregates, which are composed of up to tens of thousands of molecules, makes a straightforward interpretation of their infrared spectra difficult or even impossible. The present thesis makes use of a combination of a quantum mechanical model for the calculation of the vibrational spectra — the extended vibrational exciton model — and a molecular dynamics approach for the generation of the particle structures. Calculations are performed for pure and mixed aggregates containing NH₃,SF₆, C0₂,CO, and CHF₃.With a microscopic model at hand, it becomes even possible to go beyond system specific effects to uncover general underlying trends.

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