Zero Kinetic Energy Photoelectron Spectroscopy of Polycyclic Aromatic Hydrocarbons

Graduation date: 2016In this dissertation, I describe spectroscopic studies of jet-cooled polycyclic aromatic hydrocarbons (PAH) and one nitrogen substituted PAH (PANH) using pulsed field zero kinetic energy (ZEKE) photoelectron spectroscopy and resonantly enhanced multiphoton ionization (REMPI) spectroscopy. Recently, there has been a demand for far-infrared (FIR) spectral information of astrophysically relevant molecules by the National Aeronautics and Space Administration (NASA). Concurrent with the launching of the Herschel Space Observatory and the Stratospheric Observatory for Infrared Astronomy (SOFIA), NASA is on a mission to map out the chemical composition of the interstellar medium. In response to this call and in answering a broader interest in modeling the energy balance of the astrophysical environment, we have initiated a systematic study of polycyclic aromatic hydrocarbons, concentrating on the vibrational information in the FIR for the first electronically excited state and for the ground electronic state of the cation. From the REMPI experiment, we have learned that the vibronic structure of small stable PAHs generally follows the Franck-Condon principle, but vibronic coupling is prevalent for most larger sized PAHs. Nitrogen substitution can affect the nature of the electronic states and hence the vibronic distribution of the REMPI spectrum and ultimately the ZEKE spectra. Different from REMPI, ZEKE spectra typically follow the Franck-Condon principle, and spectral simulations using the Gaussian software package can typically reproduce the ZEKE spectrum obtained from the origin of the electronic transition qualitatively. Although ZEKE does not offer direction infrared transition intensities, our spectroscopic information in the FIR can benchmark theoretical values and offer guidance for NASA's astrophysical missions