The Crabtree group uses laboratory spectroscopy coupled with quantum chemical calculations and astronomical observations to understand the formation and evolution of molecules in space. Powerful telescope facilities, such as the Hubble Space Telescope and the Atacama Large Millimeter Array (ALMA), provide spectacular data about astronomical objects like interstellar clouds and protoplanetary disks, but challenging experimental work that simulates the extreme conditions of space is required in order to accurately interpret these observations. We currently work on four main projects to meet these challenges:
- Discovery of new radicals
The interstellar medium contains many exotic molecules, including ions and radicals. We use techniques in microwave spectroscopy together with plasma sources to create these molecules and characterize their unique spectral signatures so that they can be identified and studied in space. In addition, we perform quantum chemical calculations of the structures of these molecules to aid in the interpretation of their spectra. Expanding the chemical inventory of reactive molecules in different regions of space gives new insight into the physical and chemical processes at play in the universe.
- Low-temperature kinetics
Many places where molecules are observed in space are cold by terrestrial standards (<100 K vs 298 K), yet few chemical reactions have been studied at such low temperatures. Accurate simulations of chemistry in space require data on reaction rates low temperature. We combine microwave spectroscopy with advanced molecular beam methods to simulate astronomical environments and monitor chemical reactions under those conditions. Our principal objectives are to explore new routes to the formation of prebiotic molecules in astrophysical environments.
- New methods in infrared spectroscopy
To complement our efforts on radical discovery, we are developing new highly-sensitive and selective methods in laser spectroscopy to measure their high resolution infrared spectra. We use a unique liquid-nitrogen-cooled plasma cell to generate exotic species, and then probe them with a state-of-the-art optical parametric oscillator laser that is locked to an optical cavity and frequency modulated. This spectrometer can be used with velocity modulation techniques to selectively detect ions or with Zeeman modulation to selectively detect radicals.
- Photodissociation of transient diatomics
Diatomics are the most abundant class of molecules in space, and in many regions the main way they are destroyed is via photodissociation by ultraviolet light. In collaboration with Professors Cheuk-Yiu Ng and Lee-Ping Wang, we use both ab initio quantum chemistry and velocity map imaging techniques to determine the photodissociation cross sections for diatomic molecules that are not stable under terrestrial conditions. The cross sections we obtain are essential for modeling the chemistry of the interstellar medium and protoplanetary disks