Infrared Spectroscopy of Carbon Dioxide and Water Molecular Clusters

This dissertation discusses energy transfer processes in cryogenic liquids, and infrared spectroscopy of molecular clusters. An overview of each chapter's content will be presented here. Chapter 1 is a brief summary of energy transfer work involving an optically pumped CO doped liquid argon solution. Experiments were performed using a cw-infrared laser to optically pump the nu = 0 tonu = 1 vibration in CO. Rapid energy transfer between the vibrationally excited CO molecules resulted in some of the CO present containing in excess of nu = 30 vibrational quanta. Chapter 1 discusses two main results obtained by studying these high vibrational states. Namely, overtone intensity enhancement was observed as compared to the corresponding transitions in the gas phase, and the ability of these high vibrational states to undergo chemical reaction was demonstrated. Chapters 2 and 3 explore various aspects regarding the collective vibrations of molecular clusters. Chapter 2 presents a theoretical model which allows the infrared absorption spectrum to be calculated for an arbitrary cluster system by knowing only isolated molecule properties and an appropriate pair-wise interaction hamiltonian. Chapter 3 illustrates the usefulness of this theory by calculating the infrared spectra corresponding to monolayer coverages of CO on NaCl (100) as well as the nu_3 -infrared spectra corresponding to 3-dimensional gas phase CO_2 clusters. Finally, chapters 4 and 5 discuss experiments that have generated gas phase clusters. Various properties of CO_2 and H_2O clusters are discussed, such as cluster size and causes of structure in the infrared spectra. Also, the kinetics of cluster formation and the dynamics of cluster disappearance is explored.