UC Davis

Through my time in graduate school, I have worked on three different gas phase spectroscopy research projects, performed on three unique and different apparatuses, all with astronomical relevance. At the center of these projects is the question, how life came to be on Earth. My research aims to help answer this question by studying reactions and molecules involved in the formation of complex organic molecules (COMs), which are thought to have been involved in the prebiotic/biotic chemistry on Earth and provided much of the organic material in the solar system.

To learn about the formation of COMs, it is necessary to learn about the formation of small molecules that may have played a role in the formation of COMs (project 1), be able to detect these molecules using radio telescopes (project 2), and learn about the environments where they are found (project 3).

Small molecules, such as CO, which may have played a role in the formation of COMs, are thought to have formed in the interstellar medium (ISM) through ion-molecule reactions since these reactions are barrierless and exothermic. To better understand these reactions, my first project was to study 2 ion-molecule reactions. Specifically, I studied the chemical reactivity of vanadium cations with methane and with water as a function of the quantum spin-orbit electronic state of the vanadium cation as well as a function of the center of mass collision energy. The vanadium cation, which is a relevant example for understanding ion reactions in general, was prepared into thirteen electronic states. The vanadium was ionized by two-color vis-UV lasers and prepared into the desired quantum spin-orbit electronic state through a pulsed field ionization-photoion process, then passed through two quadrupoles and two octupoles into the reaction chamber filled with either methane or water, and the formed products were detected by a modified mass spectrometer. From this, the reaction channels at different center of mass collision energies were determined. The triplet state was shown to be more reactive than the quintet states for both methane and water, while the J-state was found to have no influence on reactivity.

While ion-molecule reactions are able to form small molecules found in the ISM, they have not been able to form larger molecules such as COMs. A proposed reaction pathway to form COMs is through radical-neutral and radical-radical reactions occurring on icy grain mantels in space. In order to predict what reactions may occur in space, it is necessary to know what radicals and other molecules may be in the ISM. Radio telescopes, such as the Atacama Large Millimeter Array (ALMA), can detect the rotational spectra of molecules in space, but without a database to compare to, few complex radicals have been identified. To obtain the rovibrational spectra of radicals thought to be in the ISM, as my next project, I designed a technique and instrument that combines cavity-enhanced frequency modulation spectroscopy with an alternating current magnetic field generated by a solenoid. This produced a sensitive, radical-selective, and Doppler-free technique that can measure rovibrational transitions of radicals with an accuracy and precision of better than 1 MHz. This technique has been named Noise Immune Cavity Enhanced Optical Heterodyne Zeeman Modulation Spectroscopy (NICE-OHZMS).

Since it is proposed that COMs may form on icy mantles of dust grains, my final project looked at how molecules in the icy mantles, specifically water, may affect the reactivity and ionization energy of molecules embedded in these icy mantles. Complex organic molecules, such as alcohols, are thought to freeze onto these icy mantles surrounding dust grains where vacuum ultraviolet (VUV) light in the ISM can photoionize these molecules, forming radical cations that may be involved in the production of precursors to life. To better understand how water may affect ethylene glycol, which has been detected in the ISM and may embed onto these icy mantles, the fundamental interactions between ethylene glycol and water were investigated by studying ethylene glycol water clusters. As a comparison with ethylene glycol, two other diol water cluster systems were studied, specifically, 1,2-propylene glycol water clusters and 1,3-propylene glycol water clusters. The experiments were performed by forming a supsersonic molecular beam of water and the diol of interest, ionizing this with tunable vacuum ultraviolet radiation from the Advanced Light Source synchrotron, and detecting the ionized clusters using reflectron time of flight mass spectrometry. The ionizing radiation was scanned over a range of photon energies so as to provide information about the formed clusters at these photon energies and, from this, determine the appearance energy of the clusters. Clusters of both diol fragments along with unfragmented diols with water were detected and some have been visualized theoretically. It was found that the addition of the methyl group and the location of the methyl group affected the energy needed to form fragment clusters. Using theory, for certain clusters ionization energies and appearance energies were calculated.

Through these three projects, I have had the opportunity to perform both theory calculations and experiments and learn about different instruments while making a small contribution to the pursuit of how life came to be on Earth.