Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 37 for “"Isotopologues"”.
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The geochemistry of methane isotopologues
This thesis documents the origin, distribution, and fate of methane and several of its isotopic forms on Earth. Using observational, experimental, and theoretical approaches, I illustrate how the relative abundances of 12CH4, 13CH4, 12CH3D, and 13CH3D record the formation, transport, and breakdown …
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The geochemistry of methane isotopologues
This thesis documents the origin, distribution, and fate of methane and several of its isotopic forms on Earth. Using observational, experimental, and theoretical approaches, I illustrate how the relative abundances of ¹²CH₄, ¹³CH₄, ¹²CH₃D, and ¹³CH₃D record the formation, transport, and breakdown …
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The biogeochemistry of methane isotopologues in marine and lacustrine sediments
… carbon cycle. The relative abundances of methane isotopologues (e.g., 12CH4, 13CH4, 12CH3D, and 13CH3D) record process-based information about the formation conditions, transport, and fate of methane, and in select environments can serve as a temperature proxy. This geochemical tool is herein …
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The Biogeochemistry of Methane Isotopologues in Marine and Lacustrine Sediments
… carbon cycle. The relative abundances of methane isotopologues (e.g., ¹²CH₄, ¹³CH₄, ¹²CH₃D, and ¹³CH₃D) record process-based information about the formation conditions, transport, and fate of methane, and in select environments can serve as a temperature proxy. This geochemical tool is herein …
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DIURNAL VARIATION OF WATER VAPOR ISOTOPOLOGUES ON THE CHAJNANTOR PLATEAU DURING THE AUSTRAL SPRING
The diurnal variation of water vapor isotopologues over the Chajnantor Plateau during the Austral Spring was investigated using a near continuous record of in situ water vapor isotopologues, numerical modeling, and routine meteorological measurements. On average, there is an approximately 34% …
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Biological oxygen production from oxygen-to-argon ratios and oxygen isotopologues in the Atlantic Ocean
… techniques based on O2/Ar ratios and O2 isotopologues to measure net community production (N) and gross oxygen production (G) in two different areas relevant for the marine C cycle: the South Atlantic subtropical gyre and the North Atlantic during a spring bloom. The former despite small …
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Trace gases in Antarctic and Greenland firn and ice: a record of carbonyl sulphide and the isotopologues of chlorofluorocarbons
Through the industrial revolution of the last 250 years, trace gases have had a significant impact on the climate. Of particular relevance to this work are species which facilitate the destruction of stratospheric ozone. In this thesis, I focus on four of these species. Understanding the release, …
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The Isotopic Composition of Water Vapor in the Upper Troposphere/Lower Stratosphere Region : Modeling, Analysis and Sampling
… of atmospheric water vapor. The stable isotopologues - $HDO$, $H_2^{17}O$ and $H_2^{18}O$ - and the radioactive isotopologue $HTO$ are discussed. A complete analytical procedure has been developed for the purpose of precise measurements of the mentioned water isotopologues. For the …
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Stabilization dynamics of the ozone molecular system
… larger-than-expected concentrations of heavier isotopologues of ozone known as 'ozone isotopic anomaly' in the stratosphere is a mass-independent effect (in contrast to most kinetic isotope effects familiar to chemists) that is traced back to the recombination process in the formation of ozone …
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Isotopes as a Tool for Exploring Exoplanet Atmospheres
… we can characterize exoplanet atmospheres using isotopologues. I also extend this to the detectability of novel biosignature gases by way of carbon isotope ratios. I evaluated the detectability of ¹³CO₂ in the atmospheres of temperate terrestrial and sub-Neptune sized planets and assess its …
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Experimental investigations of isotopologue fractionation during microbial methanogenesis
… as well as the abundance of methane clumped isotopologues ([delta]¹³CH₃D) during microbial methanogenesis. Chapter 2 uses batch and fed-batch culturing systems to investigate the effects of H₂ concentrations on isotopologue fractionation. The results from fed-batch experiments confirmed the …
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Molecular Spectroscopy: A Study of Molecules in Earth and Planetary Atmospheres
<p>The four most abundant isotopologues (N<sub>2</sub>O, <sup>15</sup>NNO, N<sup>15</sup>NO, and NN<sup>18</sup>O) of nitrous oxide have been measured in the Earth's atmosphere by infrared remote sensing with the Atmospheric Chemistry Experiment (ACE) Fourier transform spectrometer. These satellite …
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Experimental, geochemical and isotopic insights on melting and degassing behavior on Earth
… 1 explores the systematics of methane (CH4) isotopologues in geothermal systems, with a particular focus on the kinetics of isotopic exchange reactions in the vicinity of the supercritical point of water (373°C and 220 bars). This study finds that CH4 isotopologues uniquely record …
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Observing residual structure in disordered peptides with multidimensional infrared spectroscopy
… stabilize a p-hairpin fold. For this work five isotopologues of TZ2 were synthesized, the p-turn label K8, the midstrand labels T10 and T3T1O, the N-terminal label S1, and the unlabeled peptide UL. Temperature dependent FTIR and 2D IR studies in conjunction with modeling revealed that the TZ2 …
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Trend Analyses of the Abundances of Atmospheric Molecules
… (δ value) distributions of the ozone isotopologues 16<sub>O</sub>16<sub>O</sub>18<sub>O</sub>, 16<sub>O</sub>18<sub>O</sub>16<sub>O</sub> and 16<sub>O</sub>17<sub>O</sub>16<sub>O</sub> were obtained. Asymmetric ozone (16<sub>O</sub>16<sub>O</sub>18<sub>O</sub>) shows higher …
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The detection and characterisation of novel alkyl spin-adducts of PBN and its derivatives using capillary gas chromatography coupled to electron-ionisation mass spectrometry
… findings have been supported using deuterated isotopologues and PBN derivatives to aid in the understanding of the reaction mechanisms and structures.
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Characterisation of a Cavity Ring-Down Spectrometer for measuring CO2, CH4, delta13CO2, and delta13CH4 in ambient air
… greenhouse gases CO2 and CH4, along with their isotopologues 13CO2 and 13CH4, are the basis for estimating the atmospheric CO2 and CH4 fluxes on high temporal resolution and for identifying their sources and sinks. The Cavity Ring-Down Spectrometer (CRDS) G2201-i measures 12CO2, 13CO2, 12CH4, …
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Investigation of phosphonate biosynthesis: I. Structure of dehydrophos II. Mechanism of hydroxyethylphosphonate dioxygenase
… oxygen for activity. Studies with substrate isotopologues and substrate analogues have given insight into the mechanism and suggest a hydroperoxylation mechanism for the early steps.
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High pressure surface enhanced Raman scattering spectroscopy
… high pressures (1-4 GPa). The molecules were two isotopologues of the dye rhodamine 6G (R6G and d4-R6G), adsorbed on colloidal Ag particles immobilized in polyvinyl alcohol (PVA). The distributions of pressure-induced blueshifts and linewidths of individual molecules were obtained at different …
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Multi-mode two-dimensional infrared spectroscopy of peptides and proteins
… anharmonic potential of the amide vibrations of isotopologues of N-methylacetamide arise from significant change in the local mode composition of the amide II band due to isotopic substitution of the peptide group. Extension of multi-mode 2D IR to study the amide I'-II' spectra of an ideal …
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