Abstract
Phosphorus (P) compounds play a vital rule in living processes and are essential not only for hereditary processes, but for the growth, development, and maintenance of all plants and animals. Current biogeochemical models do not include an atmospheric component for the phosphorus cycle, except for phosphate ions incorporated in aerosols. In 2003, experimental measurements proved that volatile phosphine, PH3, exist in the atmosphere and that is has a long life-time. P is in its most reduced state in PH3 and is predicted to undergo oxidizing reactions due to the oxidizing nature of the atmosphere. Hence, we must introduce a volatile atmospheric component to the general biogeochemical P-cycle. It is a near-impossible task to identify individual molecules in the atmosphere without prior knowledge of their structures and spectra. In this thesis, we offer theoretical investigation and establishment of the volatile atmospheric P-cycle. We have calculated harmonic and anharmonic frequencies and intensities of the fundamental vibrational transitions using the normal mode model and calculated anharmonic frequencies and intensities of the OH-stretching fundamental and overtone transitions with the local mode model. We have calculated electronic absorption spectra within the vertical excitation approach using coupled cluster response methods and time dependent density functional methods with correlation consistent basis functions. We have calculated the reaction energetics and reaction rate constants for oxidation and photodissociation reactions thought to be important in the atmosphere. Furthermore, we have investigated the challenges of calculating the spin-forbidden vertical electronic transitions induced by spin-orbit coupling. We have calculated these transitions for a number of important atmospheric molecules with the DFT and CCSD quadratic response theory. Where possible we compare our theoretical results to experiment, and in the absence of experimental data we suggest that our theoretical finding may lay the ground for relevant experimental measurements.