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)来精确测量双同位素取代甲烷(13CH3D)的丰度，作为地质环境中甲烷来源的新的和可靠的替代物。在第一阶，13CH3D丰度将指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聚集同位素效应，可用于指纹独特的过程，如已看到的13C16O18O系统。该QCLAS仪器已经安装在PI的实验室中，对甲烷的四种主要同位素(12CH4、13CH4、12CH3D和13CH3D)的测量精度已达到0.1到0.5 Permil。该项目的目标是进一步优化QCLAS和样品进样系统，并使用热搅拌甲烷(200°C)和微生物产生的甲烷(100°C)校准13CH3D集束同位素测温标尺。一些地质甲烷的分析将作为先导研究。可调谐激光光谱分析是一项新兴的新技术，只是最近才应用于稳定同位素地球化学领域。这项研究探索了它在精确测量同位素物种方面的应用，这些同位素物种在技术上受到传统磁扇区-同位素比质谱仪的挑战。这项新技术的应用并不局限于13CH3D，它还可以应用于其他块状同位素体系(如二氧化碳、N2O和SO2)。拟议的项目将促进Aerodyne Inc.(美国小企业)和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，开发新一代同位素监测设备。一名研究生将积极参与开发，并接受培训，成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。这个项目将包括在本科生的课堂材料中。该项目还通过开发一种仪器，帮助增加科学基础设施，该仪器将供麻省理工学院内外的研究人员使用。非技术描述。甲烷既是一种替代能源，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，它很可能在未来我们能源资源的多样化方面发挥重要作用。进一步采集甲烷有可能增加向大气中释放的甲烷，这可能会影响气候。本提案中概述的项目是为了开发一种新的、成本较低的方法来测量来自自然来源(例如湿地、永冻土)和人为来源(例如农业)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.