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

技术说明。在这个项目中，我们应用量子级联激光红外吸收光谱（QCLAS）精确测量丰度的双同位素取代的甲烷（13 CH 3D）作为一个新的和强大的代理在地质环境中的甲烷来源。 在第一级，13 CH 3D丰度将指示甲烷产生或内部平衡其13 C-D键丰度的温度。 在第二级，动力学过程可以产生不同的聚集同位素效应，可以用于指纹独特的过程，如已经看到的13 C16 O 18 O系统。 QCLAS仪器已经安装在PI的实验室中，并且对于甲烷的四种主要同位素（12 CH 4，13 CH 4，12 CH 3D和13 CH 3D）已经实现了0.1至0.5 permil的精度。 该项目的目标是进一步优化QCLAS和进样系统，并通过使用热扰动甲烷（200 °C）以及微生物产生的甲烷（100°C）校准13 CH 3D聚团同位素测温标度。 可调谐激光光谱技术是近年来才在稳定同位素地球化学领域得到应用的一项新兴技术。 本研究探讨了其应用于同位素物种的精确测量，这在技术上具有挑战性的传统磁扇区同位素比质谱仪器。 这种新技术的应用不限于13 CH 3D，并且它可以应用于其他聚集的同位素体系（例如，CO2、N2 O和SO2）。 拟议的项目将促进Aerodyne Inc. (US小企业）和麻省理工学院，以及其他美国和国际合作者，用于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，在这一新兴的光学技术方面具有强大的仪器背景。此专题将被纳入本科课程教材。 该项目还有助于通过开发一种仪器来增加科学基础设施，该仪器将提供给麻省理工学院及其他地区的研究人员。非技术说明甲烷既是一种替代能源，也是一种强效温室气体。它很可能在未来通过水力压裂等新的收获技术实现能源资源多样化方面发挥重要作用。 进一步收集甲烷有可能增加甲烷向大气的释放，这可能会影响气候。 本提案中概述的项目是开发一种新的低成本方法，以测量自然来源（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。 这些测量可以为我们提供更好地了解甲烷循环，这可能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.