| Structure and dynamics of molecules and their surrounding environments are important subjects of chemistry and biology. Infrared spectroscopy is a great tool to study these topics, but it suffers from overlapping resonances and qualitative dynamical information. Two-dimensional infrared (2D IR) spectroscopy is a great improvement of traditional IR spectroscopies because it enhances structural resolutions, quantifies dynamics and provides coupling information. Currently, most 2D IR spectroscopies are based on third-order nonlinear processes. My dissertation is devoted to developing 2D and 3D IR spectroscopies employing fifth-order nonlinear processes.; First, a model coupled oscillator system, Ir(CO)2(C5 H7O2), was studied using a pulse sequence that probes the eigenstate energies up to the 2nd overtone and combination bands, thereby providing a more rigorous potential energy surface of the coupled carbonyl modes than can be obtained with 3rd-order spectroscopy. Furthermore, the pulse sequence is designed to generate and then rephase a two-quantum coherence to improve the resolution, which is not possible with 3rd-order techniques.; The same pulse sequence was then used to measure our first series of heterodyned 3D IR spectra. High time accuracy and phase stability are essential to 3D IR spectroscopy. We report a passive method which uses wedged optics to obtain sub-femtosecond pulse delay resolution and reference measurements for phase corrections. These improvements make 3D IR spectroscopy possible. 3D IR spectra are measured for three model systems: W(CO)6 in hexane, azide in an ionic glass, and Ir(CO)2(C5H7O 2) in hexane and chloroform. The 3D IR spectra exhibit spherical features for homogeneously broadened vibrational modes and elongated cigar-like features for inhomogeneously broadened systems. The spectra can be visualized as a series of planes appearing at the overtone and combination band frequencies. In a typical 2D IR spectrum, both diagonal peaks and cross peaks appear in the same plane, but in 3D IR spectroscopy they are separated into different 2D planes, greatly improving the spectral resolution. Simulations of the 3D IR spectra are also presented and future improvements to the technique are discussed. |
