Computer simulation of infrared spectra and structures of molecular nanoparticles

• Main Author: Firanescu, George
• Language: English
• Published: University of British Columbia 2010
• Online Access: http://hdl.handle.net/2429/22485

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.