Spectroscopy and chemistry of hydrogen bonded organic acids

In this thesis I present the results of experiments examining the vibrational spectroscopy of alpha-ketoacids, pyruvic acid (H3CCOCOOH) and glyoxylic acid (HCOCOOH), to investigate the relationship between intramolecular hydrogen bonds and chemical reactivity. Experimental spectroscopic results are supported by the theoretical work of Prof. Rex Skodje and his research group. The results are discussed in the context of atmospheric chemistry to understand the possible photochemical reaction pathways of pyruvic acid and glyoxylic acid, which serve as models for highly oxygenated compounds.;I obtained the vibrational spectrum of pyruvic acid in the mid-IR spectral region and recorded several OH vibrational overtones in the near-IR and visible spectral regions. Pyruvic acid has two rotational conformers populated at room temperature; the difference between these conformers is the position of the acidic hydrogen and an associated hydrogen bond. The frequencies and intensities are discussed for the observed transitions, placing special emphasis on the line-width of transitions affected by the intramolecular hydrogen bond in the most stable conformer. Probing the OH stretching mode of the two conformers allowed for an analysis of the differences in the potential energy surfaces caused by the hydrogen bond. The experimental linewidth, examined with theoretical calculations, was attributed to very fast chemical reaction. I also investigate the product distributions and reaction rates for pyruvic acid with varying amounts of water to highlight differences between the dry gas-phase reaction and the photochemical reaction in the presence of water.;Due to the water vapor present in the atmosphere, aldehydes and ketones are known to undergo reactions and form geminal diols. I present the first gas-phase spectrum of such a diol in a study of the equilibrium between glyoxylic acid (HCOCOOH) and its monohydrate, CH(OH)2COOH. I assign the fundamental vibrational spectrum of the glyoxylic acid monohydrate with the aid of theoretical calculations. Additionally, the OH stretching modes of both glyoxylic acid and the monohydrate were probed in order to observe the fast energy decay from hydrogen bonded OH stretching modes by analyzing the frequencies, intensities, and linewidths of the transitions. I discuss the atmospheric ramifications of the diol equilibrium and the possible competition between overtone-induced photochemistry and electronic state photochemistry. I discuss the implications to secondary organic aerosol formation and atmospheric modeling due to the new evidence regarding gas to particle phase partitioning of aldehydes.;I also investigated the excited electronic state photochemistry of pyruvic acid. By varying the amount of water in the reaction cell, I compared the reaction rates and quantum yields to note changes in the chemistry caused by the presence of water. The formation of the geminal diol removes the available electronic transition from the spectrum. However, according to theoretical calculations the hydrated clusters of pyruvic acid may have a lower energy barrier for reaction. Using IR spectroscopy, I monitored the gas-phase constituents to observe changes in the product distributions and reaction rates in the presence of gas-phase water. The photochemical reaction of pyruvic acid in the gas phase has been well-studied, as well as the UV-photochemistry of pyruvic acid in bulk water. With this study, I sought to bridge the gap between the gas phase and the solution phase. In solutions pyruvic acid is open to ion mechanisms which are not present in the gas phase, and are also not available in the limited water regime of small clusters. I found that the product distribution is similar between the gas phase and the water clusters; however the clusters do impede the rate of reaction. This is in part attributed to energy redistribution and evaporation of the clusters, and partly due to the structure of the pyruvic acid - water clusters.