Picosecond dynamics of condensed and gas phase molecules using ultrafast vibrational spectroscopy

Abstract

This thesis describes the use of linear and nonlinear vibrational spectroscopy ina variety of chemical systems. This work will first highlight the necessary theoretical background for understanding and interpreting the results of nonlinear spectroscopic experiments such as two-dimensional infrared (2D-IR) spectroscopy. 2D-IR spectroscopy is a technique that reports on the femtosecond to picosecond timescale dynamics that are relevant for processes such as solvent reorganization and vibrational energy redistribution. Next, this work presents the use of multiple vibrational spectroscopy techniques to better understand the solvation environment of N3 and Z907 dyes, which are commonly studied for use molecules in dye sensitized solar cells. It is shown that vibrational modes of functional groups on the molecule can be used as sensitive probes for changes in the environment surrounding the molecules. It is further demonstrated that these vibrational modes can report on differences in the dynamics of the solvent under changing solvent compositions. Furthermore, the theory of 2D-IR spectroscopy is extended to the gas phase. In the gas phase, it is important to take into consideration the effects of rotationally coherent states during the experiment. While polarization has been a commonly used tool in the 2D-IR spectroscopy community in the past, rotational coherences lead to a different dependence of the 2D-IR spectrum in the gas phase than one observes in the condensed phase. This work presents the theory for the use of polarization control of multiple laser pulses in order to selectively suppress signals within the 2D-IR spectrum. It further uses CO2(g) in order to demonstrate the effects of multiple polarization schemes and experimental setups on the measured 2D-IR signals.