Abstract
Simultaneous analysis of carbon dioxide isotopologues involved in the isotope exchange between the doubly substituted 13C16O18O molecule and 12C16O2 has become an exciting new tool for geochemical, atmospheric and paleoclimatic research with applications ranging from stratospheric chemistry to carbonate-based geothermometry studies. Full exploitation of this isotope proxy and thermometer is limited due to time consuming and costly analysis using mass spectrometric instrumentation. Here, we present an all optical clumped CO2 isotopologue thermometer with capability for rapid analysis and simplified sample preparation. The current development also provides the option for analysis of additional multiply-substituted isotopologues, such as 12C18O2. Since the instrument unambiguously measures all isotopologues of the 12C16O2 + 13C16O18O rightleftharpoons 13C16O2 + 12C16O18O exchange, its equilibrium constant and the corresponding temperature are measured directly. Being essentially independent of the isotope composition of the calibration gas, an uncalibrated working reference is sufficient and usage of international calibration standards is obsolete. Other isotopologues and molecules can be accessed using the methodology, opening up new avenues in isotope research. Here we demonstrate the high-precision performance of the instrument with first gas temperature measurements of carbon dioxide samples from geothermal sources.
Highlights
Simultaneous analysis of carbon dioxide isotopologues involved in the isotope exchange between the doubly substituted 13C16O18O molecule and 12C16O2 has become an exciting new tool for geochemical, atmospheric and paleoclimatic research with applications ranging from stratospheric chemistry to carbonate-based geothermometry studies
As a reference we use our evaluations of K1 from partition functions determined as direct sums and from the BMU method with harmonic frequencies and zero-point energy (ZPE) values given by Wang et al.[22]
New advances in laser absorption spectroscopy, such as evidenced by the recent measurement of 12C16O17O at the precision level of 10 ppm within a time frame of 10 min[52], indicate that laser instruments will favourably compete with mass spectrometer technology very soon
Summary
Received: 4 September 2018 Accepted: 22 February 2019 Published online: 18 March 2019. Simultaneous analysis of carbon dioxide isotopologues involved in the isotope exchange between the doubly substituted 13C16O18O molecule and 12C16O2 has become an exciting new tool for geochemical, atmospheric and paleoclimatic research with applications ranging from stratospheric chemistry to carbonate-based geothermometry studies. Full exploitation of this isotope proxy and thermometer is limited due to time consuming and costly analysis using mass spectrometric instrumentation. Reaction (R1) involves only a single chemical compound, but could not be exploited scientifically until recently This is because their very low natural abundance hampers the study of multi-substituted isotopic molecules, such as 13C16O18O, containing two or more rare isotopes (e.g. 13C and 18O) simultaneously. The achieved precision level of 200 ppm, remains still well above the commonly accepted threshold of 100 ppm (or 0.1‰) required for the study of clumped isotope fractionation in non-hydrogenated molecules
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