An ultraviolet Raman wavelength for the in-situ analysis of organic compounds relevant to astrobiology

A UV Raman instrument holds great promise for future in-situ astrobiology investigations on Mars and elsewhere in the solar system due to its potential for high organic sensitivity, stand-off detection, and detection on unprepared samples. We characterize the fluorescence spectra of a range of organic compounds including amino acids, fatty acids, alkanes, and polycyclic aromatic hydrocarbons (PAHs) at three UV excitations to determine at what Raman excitation fluorescence is minimized. Both Raman and fluorescence measurements indicate that a Raman instrument operating with an excitation of 266 nm will result in less fluorescence compared to an excitation of 355 nm. Raman spectra of organic compounds at a 1% concentration in a silica sand matrix are obtained at an excitation wavelength of 266 nm, and demonstrate either an absence of fluorescence or a reduction of fluorescence to a magnitude on the order of the Raman intensity, increasing the sensitivity of the instrument to organic compounds.