We located interstellar organics from a CR1 chondrite with NanoSIMS and analyzed FIB-extracted sections with XANES. D-rich material appears not associated with a functional group, whereas 15N-rich matter shows some affinity to nitrile functionality

Alexander, C. M. O'D.

Busemann, H.

Cody, G. D.

Kilcoyne, A. L. D.

Nittler, L. R.

Stroud, R. M.

Yabuta, H.

Zega, T. J.

English

Open Research Online (The Open University)

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsSecondary ion mass spectrometry and x-ray absorptionnear-edge structure spectroscopy of isotopicallyanomalous organic matter from CR1 chondrites GRO95577Conference or Workshop ItemHow to cite:Busemann, H.; Zega, T. J.; Alexander, C. M. O’D.; Cody, G. D.; Kilcoyne, A. L. D.; Nittler, L. R.; Stroud,R. M. and Yabuta, H. (2007). Secondary ion mass spectrometry and x-ray absorption near-edge structure spectroscopyof isotopically anomalous organic matter from CR1 chondrites GRO 95577. In: 38th Lunar and Planetary ScienceConference, 12-16 Mar 2007, League City, Texas, USA.For guidance on citations see FAQs.c© [not recorded]Version: [not recorded]Link(s) to article on publisher’s website:http://www.lpi.usra.edu/meetings/lpsc2007/pdf/1884.pdfCopyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyrightowners. For more information on Open Research Online’s data policy on reuse of materials please consult the policiespage.oro.open.ac.ukSECONDARY ION MASS SPECTROMETRY AND X-RAY ABSORPTION NEAR-EDGE STRUCTURE SPECTROSCOPY OF ISOTOPICALLY ANOMALOUS ORGANIC MATTER FROM CR1 CHONDRITE GRO 95577.  H. Busemann1,2, T. J. Zega3, C. M. O’D. Alexander2, G. D. Cody4, A. L. D. Kilcoyne5, L. R. Nittler2, R. M. Stroud3, H. Yabuta4, 1Planetary & Space Science Research Institute, The Open University, Milton Keynes, MK7 6AA, UK, h.busemann@open.ac.uk, 2Department of Terrestrial Magnetism, Carnegie Institution of Washing-ton, USA, 3Materials Science and Technology Division, Naval Research Laboratory Washington DC, USA, 4Geophysical Laboratory, Carnegie Institution of Washington, USA, 5Chemical Science Division, Lawrence Berke-ley National Laboratory, Berkeley, USA.   Introduction:  Primitive meteorites contain abun-dant (2–5 wt%) carbonaceous material. At least some of this, mostly insoluble organic matter (IOM), is likely to have originated in the protosolar molecular cloud, based on its spectral properties and H and N isotope characteristics [1–4]. The complete characteri-zation of this IOM will hence improve our understand-ing of: (i) chemistry in interstellar space, (ii) processes that occurred during incorporation of interstellar IOM into the first solar system bodies, and (iii) parent-body processing of the IOM.  The synthesis, molecular structure and alteration mechanisms of the IOM are mostly unknown and dif-ficult to assess. Particularly helpful in this regard may be spatially correlated studies, where isotope anoma-lies in H and N, detected with Secondary Ion Mass Spectroscopy (SIMS), locate interstellar material that can then be analyzed with Micro-Raman Spectroscopy, Scanning Transmission X-Ray (STXM) and Transmis-sion Electron (TEM) Microscopy. Samples:  Here we discuss correlated examina-tions of IOM from the CR1 chondrite GRO 95577. This meteorite contains the as-yet most primitive IOM of any chondrite we have studied, based on Micro-Raman Spectroscopy, bulk IOM H and N isotopic analyses and isotope mapping [4–6]. See [5] for the method of IOM extraction. SIMS Analyses:  We mapped the H, C, and N (as CN−) isotopic compositions of 10 fragments of the GRO 95577 IOM, pressed into Au substrates, with the Cameca NanoSIMS 50L at the Department of Terres-trial Magnetism (nominal resolution 100 nm). All fragments show large positive D and 15N isotope anomalies in bulk and in hotspots comparable and ex-ceeding those found in the IOM of EET 92042 (CR2) and in the matrix of Bells (anomalous CM) [4]. One fragment (Fig. 1A) has the largest directly measured δD value (41,000±9000 ‰) reported for any extrater-restrial material in the laboratory and approaches the ~50,000 ‰ value inferred for a hotspot in one inter-planetary dust particle (IDP) [7]. Fig. 1B shows a small “region of interest” (ROI) with a large δ15N value of ~1800 ‰. Many other ROIs have anomalies in δD in the range 5000-20,000 ‰. The fragment in Fig. 1C contains five ROIs that show spatially corre-lated enrichments in D and 15N. Three of them also show depletions in 13C (not shown). We selected these three, isotopically most interesting, aggregates for Fo-cused Ion Beam lift out (FIB) and x-ray spectroscopy. FIB extraction:  The ROIs discussed above have been lifted out with the Naval Research Laboratory FEI Nova 600 FIB-SEM microscope equipped with an Ascend Instruments Extreme Access lift-out tool [8]. Five sections of ~3-15 μm (Fig. 1) were extracted with a 30 keV Ga+-ion beam, thinned to ~200 nm and lifted out with micro-tweezers fabricated in situ. The protec-tive Pt straps covering the IOM are visible in Figs. 1A-C. Fig. 1D shows the excavated sections of the frag-ment in Fig. 1C before lift out.    Fig. 1A-C: SEM micrographs (15 keV, mag 2500-5000) of 3 fragments of GRO 95577 IOM, showing the Pt protective straps and overlaying NanoSIMS δD and δ15N distribution maps. Various isotopically anomalous ROIs are indicated. D: Excavated sections from fragment in Fig. 1C with IOM sandwiched be-tween Pt and Au substrate, prior to lift out. The STXM image of the section in front (~3 μm IOM) is shown in Fig. 2. The section in the back was lost during sample handling. Lunar and Planetary Science XXXVIII (2007) 1884.pdfXANES Analyses:  We analyzed the four surviv-ing sections shown in Fig. 1 with the scanning x-ray transmission microscope (STXM) at the soft x-ray beamline 5.3.2 (optimized for ~250-600 eV) of the Advanced Light Source in Berkeley (resolution ~40 nm), both in stack image and line modes. We obtained spectra from carbon, nitrogen, and oxygen X-ray Ab-sorption Near-edge Structure (C-, N-, and O-XANES) Spectroscopy. XANES allows the determination of relative elemental abundances, as well as the func-tional group characterization of C-, N-, and O-bearing molecules [9].   Fig. 2A-C: C-XANES spectra of D-rich (top), 15N-rich and “typical” (bottom) IOM. D: STXM image (above C-edge) of fragment shown in front of Fig. 1D. E: N-XANES of D and 15N hotspots and typical IOM: a=imine, b=nitrile, c= amidyl(?), d=ionization edge.  Analysis of the XANES data is ongoing, but Fig. 2 illustrates some preliminary results. Figs. 2A-C show examples of C-XANES spectra of D (top) and 15N hotspots, as well as “typical” IOM (bottom). Most spectra are very similar and show features at ~285 and 289 eV, typical for aromatic and carbonyl functional groups. Fig. 2D shows a STXM image of the section in the foreground of Fig. 1D. Fig. 2E compares the spa-tially integrated N-XANES spectra (fragment from Fig. 1B) for D (green) and 15N (red) hotspots and “typical” IOM (blue). The three spectra show signifi-cant variations. In particular the 15N hotspot shows much higher abundance of nitrile than the other IOM regions and the D hotspot shows a stronger feature at ~401 eV, possibly due to amidyl. All O-XANES spec-tra (not shown) were similar, showing a carbonyl fea-ture at ~532 eV.  Discussion:  The better spatial resolution of the NanoSIMS compared to the 6f used in earlier studies reveals that the anomalies in D reported for meteoritic IOM of up to δD ~20,000 ‰ [4] are still lower limits. The highest δD value of 41,000 ‰ found in this study approaches the values in gaseous deuterated molecules in the cold interstellar medium [10], providing further evidence for the pristine character of the IOM and its likely origin in the protosolar cloud or outer regions of the protoplanetary disk. The IOM in GRO 95577 (CR1) appears similarly primitive to that of EET 92042 (CR2) [4−6], implying that the more extensive aqueous alteration experienced by this type 1 CR chondrite did not significantly alter the pristine charac-teristics of the IOM. The spatially correlated positive anomalies in D and 15N, and negative anomalies in 13C resemble closely the properties recently reported for nanoglobules in the Tagish Lake meteorite [e.g., 11, 4], suggesting that these, probably presolar, aggregates are also present in the primitive CR chondrites. The apparent lack of significant variations in C-XANES spectra may indicate that the most extreme D anoma-lies are not associated with any specific functional groups. Variations in the N-XANES spectra suggests, however that the 15N enrichments, originating from interstellar environments, do appear to be associated with a noticible increase in nitrile functionality; i.e. that there exists in the case of 15N a molecular carrier for this isotopic anomaly.  Further analyses of the FIB sections by TEM are planned and will be presented at the meeting. Acknowledgment:  This work has been supported by NASA’s Cosmochemistry, Origins of Solar  Sys-tems and SRLIDAP programs and the NASA Astrobi-ology Institute. References:  [1] Pendleton Y. J. et al. (1994) ApJ 437, 683–696. [2] Alexander C. M. O’D. et al. (1998) Meteorit. Planet. Sci. 33, 603–622. [3] Bradley J. et al. (2005) Science 307, 244–247. [4] Busemann H. et al. (2006) Science 312, 727–730. [5] Alexander C. M. O’D. et al. (2007) GCA 71, in press. [6] Busemann H. (2007) GCA, submitted. [7] Messenger S. et al. (2003) Space Sci. Rev. 106, 155–172. [8] Zega T. J. et al. (2007) Meteorit. Planet. Sci. 42, submitted. [9] Cody G. D. et al. (2007) EPSL, submitted. [10] Millar T. J. et al. (1989) ApJ 340, 906–920. [11] Nakamura-Messenger K. et al. (2006) Science 314, 1439–1442.  Lunar and Planetary Science XXXVIII (2007) 1884.pdf

Secondary ion mass spectrometry and x-ray absorption near-edge structure spectroscopy of isotopically anomalous organic matter from CR1 chondrites GRO 95577

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Secondary ion mass spectrometry and x-ray absorption near-edge structure spectroscopy of isotopically anomalous organic matter from CR1 chondrites GRO 95577

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