Application of quantum cascade laser-infrared absorption spectroscopy for methane clumped isotope thermometry using doubly isotope substituted methane (13CH3D)

技术描述。本项目采用量子级联激光红外吸收光谱技术（QCLAS）精确测量双同位素取代甲烷（13CH3D）丰度，作为地质环境中甲烷来源的一种新的、可靠的替代指标。在第一阶上，13CH3D丰度表示甲烷产生的温度或其13C-D键丰度的内部平衡。在第二级，动力学过程可能产生不同的团块同位素效应，可以用来识别独特的过程，如13C16O18O体系。QCLAS仪器已经安装在PI实验室中，对甲烷的四种主要同位素（12CH4、13CH4、12CH3D和13CH3D）的测量精度达到了0.1 ~ 0.5 permil。该项目的目标是进一步优化QCLAS和进样系统，并使用热炒甲烷（200°C）和微生物产生的甲烷（100°C）校准13CH3D团块同位素测温标度。一些地质甲烷将作为试点研究进行分析。可调谐激光光谱是近年来才应用于稳定同位素地球化学领域的一项新兴技术。本研究探讨了其在传统磁扇区-同位素比质谱仪技术上具有挑战性的同位素物质精确测量中的应用。这项新技术的应用不仅限于13CH3D，还可以应用于其他块状同位素体系（如CO2、N2O和SO2）。拟议的项目将促进Aerodyne公司（美国小企业）与麻省理工学院以及其他美国和国际合作者之间的密切合作，共同开发新一代同位素监测设备。一名研究生将积极参与开发，并被培训为未来的同位素地球化学家，在这一新兴的新光学技术方面具有强大的仪器背景。本课题将被纳入本科课堂教材。该项目还通过开发一种仪器来帮助增加科学基础设施，该仪器将提供给麻省理工学院和其他地方的研究人员。非技术描述。甲烷既是一种可替代能源，也是一种强有力的温室气体。通过水力压裂等新的采收技术，它很可能在未来能源资源的多样化中发挥重要作用。进一步收集甲烷有可能增加释放到大气中的甲烷，这可能会影响气候。本提案中概述的项目旨在开发一种新的、成本更低的方法来测量来自自然来源（如湿地、永久冻土）和人为来源（如农业）的甲烷中的碳和氢同位素丰度。这些测量可以让我们更好地了解甲烷循环，这可能会对甲烷的环境管理产生影响。

Technical description. In this project, we apply quantum cascade laser infrared absorption spectroscopy (QCLAS) to precisely measure abundance of doubly isotope-substituted methane (13CH3D) as a new and robust proxy for the source of methane in geologic environments. On the first order, 13CH3D abundance would indicate the temperature at which the methane was produced or internally equilibrated for its 13C-D bond abundance. On the second order, kinetic process may produce different clumped isotope effect that may be used to fingerprint unique processes, as has been seen for the 13C16O18O system. The QCLAS instrument has already been installed in the PI's laboratory and the precision of 0.1 to 0.5 permil have been achieved for four major isotopologues of methane (12CH4, 13CH4, 12CH3D, and 13CH3D). The goal of the project is to further optimize the QCLAS and sample inlet system, and calibrate the 13CH3D clumped isotope thermometry scale by using thermally scrambled methane (200 °C) as well as microbially produced methane (100°C). Some geologic methane will be analyzed as a pilot study.Tunable laser spectroscopy is an emerging new technology only recently applied in the field of stable isotope geochemistry. This research explores its application to precise measurements of isotopologue species that are technically challenging by conventional magnetic sector-isotope ratio mass spectrometry instruments. Applications of this new technology are not limited to 13CH3D, and it could be applied to other clumped isotopologue systems (e.g., CO2, N2O and SO2). The proposed project will facilitate the close collaboration between Aerodyne Inc. (US small business) and MIT, as well as other US and international collaborators, for the development of new generation isotope monitoring equipment. One graduate student will actively participate in development and be trained as a future isotope geochemist with a strong instrumental background in this emerging new optical technology. This project will be included in undergraduate class materials. This project also helps to add to scientific infrastructure via development of an instrument that will be available to researchers at MIT and beyond.Non-technical description.Methane is both an alternative energy source as well as being a potent greenhouse gas. It is likely to play a significant role in future diversification of our energy resources through new harvesting technologies such as fracking. Further harvesting of methane has the potential for increase release of methane to the atmosphere, which may impact climate. The project outlined in this proposal is for the development of a new, lower-cost method to measure carbon and hydrogen isotope abundances in methane from natural sources (e.g. wetlands, permafrost) and anthropogenic sources (e.g. agriculture). These measurements can provide us with a far better understanding of methane cycling, which may have implications for environmental management of methane.