Molecular Level Understanding of Degradation of Insensitive Munitions on Soil Proxies as the Basis for Developing Chemical Footprints
Abstract
New explosives and propellants are continuously being developed by both the U.S. and by other nations. Once in the environment, they may degrade through a number of mechanisms, forming new products. As such, their chemical signatures will be different than those of the parent munitions. Developing fingerprints to identify munitions that were used therefore requires a molecular level understanding of how these agents are transformed in the environment and how fast this occurs in various media in which they are found. Insensitive munitions (IM) such as IMX-101 are being developed that will become widely dispersed in water, on soil surfaces and as solid particles. Over the past few years, studies of the degradation of IMX-101 and its components in aqueous systems have been reported, but far less is known regarding their reactions as solids or adsorbed compounds. Studies of degradation by atmospheric oxidants (such as OH radicals) and of the gas phase products are also lacking. Thus, there are major gaps in our knowledge of IM degradation products that are central to their chemical fates and transport, and hence to assessing their environmental forensics. We propose to study reactions with OH radicals and direct photolysis of IMX-101 and its individual components as (1) thin solid films on infrared transmitting crystals and on proxies for environmental surfaces such as dust and soil, and (2) as particles suspended in air. Knowledge of gas and solid phase products generated simultaneously will provide unique molecular level insights into the mechanisms involved. These studies will also provide fundamental data such as quantum yields over three different wavelength regions that are essential for quantitative assessment of the IM lifetimes and fates in the environment under a variety of selected conditions (e.g., season, location, time of day). Effects of particle size on kinetics, products and mechanisms is an important part of the proposed research, since both size and composition can impact particle reactivity and products. These studies will additionally provide insight into organic particle composition differentiated by size and by surface versus bulk composition, a project currently funded by ARO. A variety of techniques will be applied, including Fourier transform infrared spectroscopy and mass spectrometry for loss of the parent compound and formation of solid products and gases. The mixture of solid products is likely to be sufficiently complex that separation prior to analysis by light absorption and mass spectrometry is critical. A combined ultra performance liquid chromatograph interfaced to a photodiode array detector and mass spectrometer is therefore requested. In addition, a scanning mobility particle sizer is needed to characterize and size-select the solid particles. The requested instrumentation is critical for providing specific identification and quantitative analysis in the complex mixtures of reactants and products. The results of these studies will be a better understanding of the environmental fates and forensics of IMX-101 and its components. Both this project and one currently funded by ARO address chemical fates of compounds of relevance to ARO/DoD, and provide the fundamental, molecular level understanding that is needed to predict future transformations of these compounds. This instrumentation will provide training for the next generation of scientists who will contribute to ARO/DoD research. The PI traditionally has a research group that consists of students from high school to undergraduates, graduate students, postdoctoral fellows and project scientists. They are overwhelmingly from underrepresented groups in STEM, particularly women. In addition, we share instrumentation across groups and thus it will find even broader use and provide training to many students outside the PIÕs own group.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 09, 2020
- Source ID
- W911NF2010064
Entities
People
- Barbara J. Finlayson-Pitts
Organizations
- Army Contracting Command
- United States Army
- University of California, Irvine