¹Edward Cloutis, ¹Paul Szymanski, ¹Daniel Applin, ²Douglas Goltz
¹Department of Geography, University of Winnipeg, 515 Portage Avenue, Winnipeg, Manitoba, Canada R3B 2E9
²Department of Chemistry, University of Winnipeg, 515 Portage Avenue, Winnipeg, Manitoba, Canada R3B 2E9

Polycyclic aromatic hydrocarbons (PAHs) are widely present throughout the solar system and beyond. They have been implicated as a contributor to unidentified infrared emission bands in the interstellar medium, comprise a substantial portion of the insoluble organic matter in carbonaceous chondrites, are expected stable components of organic matter on Mars, and are present in a wide range of terrestrial hydrocarbons and as components of biomolecules. However, PAH structures can be very complicated, making their identification challenging. Raman spectroscopy is known to be especially sensitive to the highly polarizable C-C and C=C bonds found in PAHs, and therefore, can be a powerful tool for PAH structural and compositional elucidation. This study examined Raman spectra of 48 different PAHs to determine the degree to which Raman spectroscopy could be used to uniquely identify different species, factors that control the positions of major Raman peaks, the degree to which induced fluorescence affects the intensity of Raman peaks, its usefulness for PAH discrimination, and the effects of varying excitation wavelength on some PAH Raman spectra. It was found that the arrangement and composition of phenyl (benzene) rings, and the type and position of functional groups can greatly affect fluorescence, positions and intensities of Raman peaks associated with the PAH backbone, and the introduction of new Raman peaks. Among the functional groups found on many of the PAHs that were analyzed, only a few Raman peaks corresponding to the molecular vibrations of these groups could be clearly distinguished. Comparison of the PAH Raman spectra that were acquired with both 532 and 785 nm excitation found that the longer wavelength resulted in reduced fluorescence, consistent with previous studies.

Reference
Cloutis E, Szymanski P, Applin D, Goltz D (2016) Identification and Discrimination of Polycyclic Aromatic Hydrocarbons Using Raman Spectroscopy. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.03.023]
Copyright Elsevier

^1,2Noemi Pinilla-Alonso et al. (>10)*
¹Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN, USA
²Florida Space Institute, University of Central Florida, Orlando, FL, USA
*Find the extensive, full author and affiliation list on the publishers website

The inner asteroid belt is an important source of near-Earth asteroids (NEAs). Dynamical studies of the inner asteroid belt have identified several families overlapping in proper orbital elements, including the Polana and Eulalia families that contain a large fraction of the low-albedo asteroids in this region.

We present results from two coordinated observational campaigns to characterize this region through near-infrared (NIR) spectroscopy. These campaigns ran from August 2012 to May 2014 and used the NASA Infrared Telescope Facility and the Telescopio Nazionale Galileo. The observations focused on objects within these families or in the background, with low albedo (pv~ ≤ 0.1) and low inclination (iP ≤ 7o). We observed 63 asteroids (57 never before observed in the NIR): 61 low-albedo objects and two interlopers, both compatible with S- or E- taxonomical types.

We found our sample to be spectrally homogeneous in the NIR. The sample shows a continuum of neutral to moderately-red concave-up spectra, very similar within the uncertainties. Only one object in the sample, asteroid (3429) Chuvaev, has a blue spectrum, with a slope (View the MathML sourceS′=−1.33± 0.21 %/1000 Å) significantly different from the average spectrum (View the MathML sourceS′=0.68± 0.68 %/1000 Å). This spectral homogeneity is independent of membership in families or the background population. Furthermore, we show that the Eulalia and Polana families cannot be distinguished using NIR data. We also searched for rotational variability on the surface of (495) Eulalia which we do not detect. (495) Eulalia shows a red concave-up spectrum with an average slope View the MathML sourceS′=0.91± 0.60 %/1000 Å, very similar to the average slope of our sample.

The spectra of two targets of sample-return missions, (101955) Bennu, target of NASA’s OSIRIS-Rex and (162173) 1999 JU3 target of the Japanese Space Agency’s Hayabusa-2, are very similar to our average spectrum, which would be compatible with an origin in this region of the inner belt.

Reference
Pinilla-Alonso N et al. (2016) Portrait of the Polana-Eulalia Family Complex: Surface homogeneity revealed from Near-Infrared Spectroscopy. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.03.022]
Copyright Elsevier

¹Ankan Das, ¹Dipen Sahu, ^2,3,1Liton Majumdar, ^4,1Sandip K. Chakrabarti,
¹Indian Centre for Space Physics, Chalantika 43, Garia Station Rd., Kolkata 700084, India
²University of Bordeaux, LAB, UMR 5804, F-33270 Floirac, France
³CNRS, LAB, UMR 5804, F-33270 Floirac, France
⁴S. N. Bose National Centre for Basic Sciences, Salt Lake, Kolkata 700098, India

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Reference
Das A, Sahu D, Majumdar L, Chakrabarti SK (2016) Deuterium enrichment of the interstellar grain mantle. Monthly Notices of the Royal Astronomical Society 455, 540-551.
Link to Article [doi: 10.1093/mnras/stv2264]