47th Lunar and Planetary Science Conference (2016) 2238.pdf

A NOVEL HIGH-MASS RESOLUTION GAS-SOURCE MASS SPECTROMETER FACILITY AT UCLA. Edward D. Young1, Issaku E. Kohl1, Kaitlyn McCain1, Junko Isa1, and Douglas Rumble III2, 1Department of Earth, Planetary, and Space Sciences, University of California Los Angeles, Los Angeles, CA, USA ([email protected]), 2Geophysical Laboratory, 5251 Broad Branch Rd. NW, Washington DC 20015-1305, USA.

Introduction: Gas-source isotope ratio mass spec- Oxygen Isotopes: Analyses of extraterrestrial trometry is one of the primary methods for obtaining samples for precise and accurate 18O/16O and 17O/16O, the highest precision isotope ratio measurements of yielding diagnostic Δ′17O values, has been hampered geological and atmospheric samples. It is the standard historically by the presence of NF+ interfering with 33 + for triple oxygen isotope ratio analysis of meteorites, O2 at mass/charge 33 in the mass spectrum. The for example. However, until very recently, advances Panorama instrument can be used to eliminate this in- in this important technology have been limited. terference by virtue of its high mass resolution (Figure Here we describe a unique and novel isotope ratio 2). In a companion abstract, we demonstrate the ad- mass spectrometer (IRMS), the Nu Instruments Pano- vantages of ground-truthing extraterrestrial oxygen rama, developed explicitly for high-mass-resolution isotope ratio measurements of rocks with this method. analysis of isotopologue ratios of gas samples. We have shown recently that this instrument improves the reliability of oxygen isotope analyses at the highest precision and accuracy. In addition, it offers the pro- spects for developing the foundations for using multi- ply-substituted gas species (CH4, N2, O2) as tracers of atmospheric processes and geochemical cycles that should prove useful for extraterrestrial environments as flight instrumentation (e.g., TILDAS) improves. Panorama: The double-focussing Panorama in- strument (Figure 1) routinely operates at a mass resolv- ing power (MRP) of 40,000 with a maximum useful MRP of ~80,000. The instrument achieves this excep- 33 + + Figure 2. Separation of O2 from NF3 on the tional MRP for a multi-collector using a Matsuda ion Panorama instrument where the latter is shown optical design with an ESA radius of 1018 mm and a schematically at fictively higher ion current for magnetic sector radius of 800 mm. Collectors com- illustration. prise 9 Faraday cups and a single channel of ion count- ing each with continuously variable collector slits. Methane Isotopologues: There is considerable in-

Quad 2 terest in the origin and evolution of methane in plane- tary science (e.g., Mars, outer solar system). One

Magnet promising new approach for sourcing methane is to (R = 800 mm) measure the excesses or deficits of the multiply- substituted isotopologues relative to the stochastic ref- Oct 1 Hex 2 ESA erence frame. We have used the Panorama to measure (R=1017.6 mm) both 13CH D/12CH and 12CH D /12CH , yielding Quad 1 3 4 2 2 4 Hex 1 9 Faraday Quad 3 13 collectors Δ CH3D and ΔCH2D2, the per mil values relative to ESA the stochastic distribution. In a collaborative effort involving multiple workers, including Barbara Sher- Source Ion counter Gas inlet (20 kV) wood-Lollar, University of Toronto, Giussepe Etiope, Istituto Nazionale di Geofisica e Vulcanologia, and Dionysis Foustoukos, Carnegie Institution of Washing- ton, we are mapping out different sources and sinks of methane in rare-isotopologue space. Results, some of Figure 1. Layout of the Panorama mass spec- which are shown for the first time in Figure 3, show trometer housed at UCLA. promise for using the rare isotopologues of methane as

47th Lunar and Planetary Science Conference (2016) 2238.pdf

indicators of reaction pathways, including tempera- rock isotope ratios where analyses can be done in the tures of formation and deviations from thermodynamic gas phase (e.g., oxygen). Future applications include 17 equilibrium. simultaneous measurements of Δ′ O and Δ47 (i.e., temperature of formation) in extraterrestrial car- 15 15 14 bonates. We are also presently measuring N N/ N2 in gas samples. While there are a number of projects related to planetary science in the works, we encourage this community to come with their own ideas for mak- ing use of this new facility (Figure 5).

Figure 3. Plot showing the positions of natural and laboratory-produced methane gas in ΔCH2D2 13 vs. Δ CH3D, where here Δ refers to deviations from the stochastic distribution of these rare isotopologues. The curve shows the relationship that holds for thermodynamic equilibrium. Black dots mark temperatures of bond formation in 50 degree increments. Temperatures in italics refer to those of the synthesis experiments. Figure 4. Rare isotopologue effects of mixing two methane samples formed at different temperatures. As shown in Figure 3, laboratory experiments pro- duce significant deviations from equilibrium for CH2D2 that reflect the detailed kinetics of CH4 for- mation. The natural samples shown here yield temper- atures of formation with minimal departures from equi- librium. The measurements shown in Figure 3 are not possible with conventional gas-source isotope ratio mass spectrometers. Sourcing methane can also be complicated by mix- ing. We show the isotope bond-ordering effects (e.g., Figure 3) of mixing two gases with distinct D/H and 13C/12C in Figure 4. There is a tell-tale departure from the equilibrium curve where a mixed source is present. This could be an important tracer of methane for- Figure 5. The Panorama instrument at UCLA. mation and the signatures of such gases can be investi- gated now with an eye towards applications in extrater- Acknowledgements: The Panorama facility was restrial environments in future. funded by the Sloan Foundation’s Deep Carbon Ob- Prospects for Users: We view this unique instru- servatory, the National Science Foundation, the De- ment as providing a proving ground for developing partment of Energy, Shell, UCLA and the Carnegie new tracers of gas formation in planetary atmospheres, Institution. developing new tracers for the origins of volatile ices, and for establishing interference-free measurements of