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Cyclohexanedione, Water, Nonlinear spectroscopy, 2DIR, Raman, Azobenzene


The original research outlined in this dissertation involves the use of novel theoretical and computational methods in the calculation of molecular volume changes and non-linear spectroscopic signals, specifically two-dimensional infrared (2D-IR) spectroscopy. These techniques were designed and implemented to be computationally affordable, while still providing a reliable picture of the phenomena of interest. The computational results presented demonstrate the potential of these methods to accurately describe chemically interesting systems on a molecular level. Extended system isobaric-isothermal (NPT) molecular dynamics techniques were employed to calculate the thermodynamic volumes of several simple model systems, as well as the volume change associated with the trans-cis isomerization of azobenzene, an event that has been explored experimentally using photoacoustic calorimetry (PAC). The calculated volume change was found to be in excellent agreement with the experimental result. In developing a tractable theory of two-dimensional infrared spectroscopy, the third-order response function contributing to the 2D-IR signal was derived in terms of classical time correlation functions (TCFs), entities amenable to calculation via classical molecular dynamics techniques. The application of frequency-domain detailed balance relationships, as well as harmonic and anharmonic oscillator approximations, to the third-order response function made it possible to calculate it from classical molecular dynamics trajectories. The finished theory of two-dimensional infrared spectroscopy was applied to two simple model systems, neat water and 1,3-cyclohexanedione solvated in deuterated chloroform, with encouraging preliminary results.