Ultraviolet-Stimulated Fluorescence and Phosphorescence of Aromatic Hydrocarbons in Water Ice

Abstract

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 a preliminary investigation into the feasibility of this concept. Specifically, fluorescence and phosphorescence of pure benzene ice and 1% mixtures of benzene, toluene, p-xylene, m-xylene, and o-xylene in water ice, respectively, were studied at temperatures ranging from ∼17 K up to 160 K. Spectra were measured from 200-500 nm (50,000-20,000 cm(-1)) while ice mixtures were excited at 248.6 nm. The temperature dependence of the fluorescence and phosphorescence intensities was found to be independent of the thermal history and phase of the ice matrix in all cases examined. All phosphorescent emissions were found to decrease in intensity with increasing temperature. Similar behavior was observed for fluorescence in pure benzene, while the observed fluorescence intensity in water ices was independent of temperature.

WATSON:In SituOrganic Detection in Subsurface Ice Using Deep-UV Fluorescence Spectroscopy

“…The study of organic material in ice through laser-induced fluorescence is well established (Bramall, 2007;Rohde and Price, 2007;Rohde, 2010;Pautler et al, 2012;D'Andrilli et al, 2017). Fluorescence techniques, including excitation emission matrices (EEMs) are capable of trace aromatic organic detection and characterization of dissolved organic matter (Bhartia et al, 2008;Barker et al, 2010;Johnson et al, 2011). However, in these and other established methods of ice analysis, bulk samples are typically melted and concentrated for analysis, resulting in a loss of the spatial context of organic deposition.…”

Subsurface In Situ Detection of Microbes and Diverse Organic Matter Hotspots in the Greenland Ice Sheet

“…Although none of the spectra are exact matches, alkyl or heteroatom-substituent substitution as well as changes of matrix conditions (water vs. ice, temperature effects) could cause changes to the reference spectra (Johnson et al , 2011 ). Thus, we can state that the spectral signals are broadly consistent with fluorescence spectra from PAHs, and that they are not similar to the fluorescent signals of microbial cells.…”

Noncontact, reagentless, nondestructive, detection of organics, biosignatures, and water

“…These probabilities, while lower, do occur and are seen as a distribution of photon emissions that can range over 20 to 40 nm. This allows for detailed analysis of single compounds using variations in temperature and solvents, electronic characteristics can be extrapolated from the fluorescence spectrum [5]. However in a mixed environment, simple extrapolations are difficult, if not impossible.…”

“…With the advent of new deep UV sources (Photon Systems Inc) and high quality deep UV optics, and the need for new life detection methods spurred on by NASA Astrobiology as well as counter-bio-terrorism, microbial detection with native fluorescence spectroscopy is making headway [1,2,[5][6][7][8][9]]. This has not only required development of new, novel instrumentation, but has also required incorporating analytical methods that have been used on other spectroscopic tools as well as development of new analysis methods.…”