Temperature and Isotope Dependent Kinetics of Nickel-Catalyzed Oxidation of Methane by Ozone.

The temperature dependent kinetics of Ni+ + O3 and of NiO+ + CH4/CD4 are measured from 300 to 600 K using a selected-ion flow tube apparatus. Together, these reactions comprise a catalytic cycle converting CH4 to CH3OH. The reaction of Ni+ + O3 proceeds at the collisional limit, faster than previously reported at 300 K. The NiO+ product reacts further with O3, also at the collisional limit, yielding both higher oxides (up to NiO5+ is observed) as well as undergoing an apparent reduction back to Ni+. This apparent reduction channel is due to the oxidation channel yielding NiO2+* with sufficient energy to dissociate. 4NiO+ + CH4 (CD4) (whereas 4NiO+ refers to the quartet state of NiO+) proceeds with a rate constant of (2.6 ± 0.4) × 10-10 cm3 s-1 [(1.8 ± 0.5) × 10-10 cm3 s-1] at 300 K and a temperature dependence of ∼ T-0.7±0.3 (∼ T-1.1±0.4), producing only the 2Ni+ + 1CH3OH channel up to 600 K. Statistical modeling of the reaction based on calculated stationary points along the reaction coordinate reproduces the experimental rate constant as a function of temperature but underpredicts the kinetic isotope shift. The modeling was found to better represent the data when the crossing from quartet to doublet surface was incomplete, suggesting a possible kinetic effect in crossing from quartet to doublet surfaces. Additionally, the modeling predicts a competing 3NiOH+ + 2CH3 channel to become increasingly important at higher temperatures.

Spectroscopic characterization of samples from different environments in a Volcano-Glacial region in Iceland: Implications for in situ planetary exploration.

Raman spectroscopy and laser induced breakdown spectroscopy (LIBS) are complementary techniques that together can provide a comprehensive characterization of geologic environments. For landed missions with constrained access to target materials on other planetary bodies, discerning signatures of life and habitability can be daunting, particularly where the preservation of organic compounds that contain the building blocks of life is limited. The main challenge facing any spectroscopy measurements of natural samples is the complicated spectra that often contain signatures for multiple components, particularly in rocks that are composed of several minerals with surfaces colonized by microbes. The goal of this study was to use the combination of Raman spectroscopy and LIBS to discern different environmental regimes based on the identification of minerals and biomolecules in rocks and sediments. Iceland is a terrestrial volcano-glacial location that offers a range of planetary analog environments, including volcanically active regions, extensive lava fields, geothermal springs, and large swaths of ice-covered terrain that are relevant to both rocky and icy planetary bodies. We combined portable VIS (532 nm) and NIR (785 nm) Raman spectroscopy, VIS micro-Raman spectroscopic mapping, and UV/VIS/NIR (200 - 1000 nm) and Mid-IR (5.6 - 10 µm, 1785 - 1000 cm-1) laser induced breakdown spectroscopy (LIBS) to characterize the mineral assemblages, hydrated components, and biomolecules in rock and sediment samples collected from three main sites in the volcanically active Kverkfjöll-Vatnajökull region of Iceland: basalt and basalt-hosted carbonate rind from Hveragil geothermal stream, volcanic sediments from the base of Vatnajökull glacier at Kverkfjöll, and lava from the nearby Holuhraun lava field. With our combination of techniques, we were able to identify major mineral polytypes typical for each sample set, as well as a large diversity of biomolecules typical for lichen communities across all samples. The anatase we observed using micro-Raman spectroscopic mapping of the lava compared with the volcanic sediment suggested different formation pathways: lava anatase formed authigenically, sediment anatase could have formed in association with microbial weathering. Mn-oxide, only detected in the carbonate samples, seems to have two possible formation pathways, either by fluvial or microbial weathering or both. Even with our ability to detect a wide diversity of biomolecules and minerals in all of the samples, there was not enough variation between each set to distinguish different environments based on the limited measurements done for this study.