A principal goal of astrobiology is to detect and inventory the population of organic compounds on extraterrestrial bodies. Targets of specific interest include the wealth of icy worlds that populate our Solar System. One potential technique for in situ detection of organics trapped in water ice matrices involves ultraviolet-stimulated emission from these compounds. Here, we report fluorescence spectra of a range of PAHs as pure solids and in water ice matrices at cryogenic temperatures. Matrix-isolated samples of polycyclic aromatic hydrocarbons (PAH) - water ice mixtures are prepared by depositing PAH vapors effusing from a Knudsen cell simultaneously with water vapor onto an optical window at ~12K. Specifically, 248.6 nm stimulated UV fluorescence of naphthalene, anthracene, phenanthrene, pyrene, chrysene, and coronene, as pure solids and in water ice respectively, were studied at temperatures ranging from 12K to 125K. All fluorescence emissions were found to decrease in intensity with increasing temperature but not fully regain intensity when restored to 12K. The spectra PAH - water ice mixtures exhibited sharp peaks with ascending size, enabling extraction of characteristic vibrational frequencies from the fluorescence spectra.

UV stimulated fluorescence studies of PAH-water ice mixtures

246th National Meeting (2013)

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