UC Santa Barbara

Microwave spectroscopy has long been the standard for sensitive and specific analysis of small organic molecules. Nearly every molecule identified in the interstellar medium was first studied on earth using microwave spectroscopy, and the technique has recently emerged as a powerful mixture analysis tool. Nearly all of this prior work was done in supersonic expansion experiments, which have cold rotational temperatures in the interaction region, but supersonic lab-frame molecule velocities, limiting total interaction time. Here, I present a variety of results using buffer gas cooled microwave spectroscopy, a different approach to achieving rotationally and translationally cold ensembles of neutral molecules. First, I demonstrate that microwave three-wave mixing, a previously demonstrated technique sensitive to molecular chirality, is also sensitive to molecules chiral only by virtue of isotope placement. Second, I discuss application of buffer-gas cooled microwave spectroscopy to the detection and characterization of gauche-isoprene, a species previously uncharacterizable in supersonic expansion techniques. The remaining chapters are dedicated to demonstration and discussion of third and fourth generation buffer gas cells for microwave spectroscopy. First, I make the most precise measurement of the energy differences between two chiral molecules ever conducted using a cryogenic tunable microwave Fabry-Perot resonator. Second, I demonstrate our ability to measure reaction rates between cold molecules, an essential piece of our understanding of interstellar chemistry. Third, I show that using the new BUGBITES technique, we can reach 880 Hz linewidths, a factor of 3 improvement over any other conventional rotational spectroscopy technique. Together, these experiments show the versatility and utility of buffer gas cells for microwave spectroscopy.