Characterization of free radicals in clathrate hydrates of pyrrole, thiophene, and isoxazole by muon spin spectroscopy

Gas hydrates have long been of interest to the petrochemical industry but there has been growing interest in potential applications for carbon dioxide sequestration and hydrogen storage. This has prompted many fundamental studies of structure and host-guest interactions, but there has been relatively little investigation of chemical reactions of the guest molecules. In previous work we have shown that it is possible to use muon spin spectroscopy to characterize H-atom-like muonium and muoniated free radicals formed in clathrate hydrates. Muonium forms in clathrate hydrates of cyclopentane and tetrahydrofuran, whereas furan and its dihydro- derivatives form radicals. The current work extends studies to clathrates hydrates of other 5-membered heterocycles: thiophene, pyrrole and isoxazole. All form structure II hydrates. In addition to the clathrates, pure liquid samples of the heterocycles were studied to aid in the assignment of radical signals and for comparison with the enclathrated radicals. Similar to...