Volume 1Metal-bearing molecules impact the chemical and physical environment of a plethora of astronomical sources such as the circumstellar envelopes of large asymptotic giant branch and red supergiant stars, the interstellar medium, and planetary atmospheres (e.g., cosmic dust and meteoric ablation of ~ 20 tons of metals per day into the Earth’s upper atmosphere). In particular, new molecules containing the refractory element aluminum (e.g. AlO, AlOH, AlNC) have recently been discovered in these environments via observational radioastronomy. Aluminum is one of the most abundant elements in the local cosmic neighborhood, existing as a constituent of gas-phase molecules as well as forming the basis of dust grains. Volume 1 of this thesis will discuss the ground state (rotational and vibrational) and electronic spectroscopy of new aluminum-bearing molecules. The ground state spectroscopy is discussed in the context of experimental and observational detection potential. The excited electronic states and photochemical pathways are of interest for both spectroscopic studies and their astrochemical impact. The ubiquitous presence of wide-ranging wavelengths of light and many diverse photochemical and photoionization pathways implicates aluminum-bearing molecules as drivers of chemical complexity in space. Additionally, the spectroscopic properties of silicon- and magnesium-bearing molecules have also been investigated, and a new bimolecular mechanism that acts as a sink for the currently undetected PS and PH diatomic molecules is presented. Volume 2 Alkene ozonolysis is a major contributor to the oxidizing capacity of the Earth’s atmosphere through the production of carbonyl oxide species known as Criegee intermediates. Criegee intermediate loss processes in the atmosphere include unimolecular decay to form hydroxyl radicals (OH), bimolecular reaction with trace species to produce highly functionalized organic molecules, and solar photolysis. Unimolecular decay of the syn-CH3CHOO Criegee intermediate proceeds through a vinyl hydroperoxide (VHP) intermediate species, yielding OH and vinoxy radical co-products. In this thesis, the role of excited electronic states and non-adiabatic dynamics in the ground state unimolecular decay of VHP is explored, as well as a new experimental detection scheme for vinoxy radicals. The photoionization of hydroperoxyethyl formate, the reaction product of syn-CH3CHOO and formic acid, is examined and the dissociation pathways to produce HO2 and OCHO fragments with daughter ions are mapped. Trajectory surface hopping simulations of the excited state photodynamics of CH2OO and syn-CH3CHOO implicate two unique conical intersections as branching points in the production of O (1D) and O (3P) atoms following electronic excitation to the bright 1ππ* state, and intersystem crossing is found to be negligible in the dissociation process following vertical excitation (i.e. at regions of the electronic absorption spectrum that mimics the absorption maximum). Finally, the rotational, vibrational, and electronic spectroscopic properties of other atmospheric molecules NH2NO2 and HOSO are calculated, and the atmospheric implications of their photochemistry are discussed.