Benzene, C6H6, is an aromatic compound identified in interstellar space and in our solar system on the organic-rich moon Titan. Benzene is a photo- and radiation-chemical product in Titan's upper atmosphere, possibly undergoing chemical reactions to form a variety of complex organic compounds. Pyridine, C5H5N, an aromatic heterocycle, has not yet been detected on Titan, but might be synthesized in its nitrogen-rich atmosphere. Studying benzene and pyridine can lead to a better understanding of how such molecules are made and evolve. Infrared (IR) analysis is one of the most powerful methods for identifying and characterizing molecules, quantifying reactions, and studying astrochemical evolution, but data at relevant temperatures are lacking. We have measured IR spectra and several physical properties of amorphous and crystalline C6H6 (9 K, 100 K) and C5H5N (11 K, 130 K), including densities and refractive indices. Furthermore, we also have determined (1) mid-IR band strengths of benzene and pyridine using FTIR spectroscopy and (2) IR optical constants n and k using our open-source software. Similar work has been done with solid cyclopropane, ethylene oxide, hydrogen cyanide, acetonitrile, propionitrile, ammonia, methylamine, and ethylamine as well. Ice samples were prepared by vapor-deposition onto either an optically flat, gold-mirror electrode on a quartz-crystal microbalance (for density measurements) or an IR-transparent substrate (for spectra, band strengths, and optical constants). Two-laser interferometry was used to determine refractive indices.

Infrared spectra and optical constants of solid benzene, pyridine, and other organics

ACS Spring Meeting 2021

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