Electron spin resonance studies on irradiated inorganic solids.
thesisposted on 19.11.2015, 08:48 by M. B. D. Bloom
Part I deals with the study of various transition metal nitrosyl complexes. The products of radiation-damage in anhydrous sodium nitroprusside are shown to be nitric oxide, trapped at sites with a strong crystal field, and the hitherto unknown pentacyanonitrosyl- ferrate (III) anion. The e.s.r parameters of the latter are compared with those of the isoelectronic d5 chromium (l) and manganese (II) pentacyanonitrosyl ions and a general trend is deduced. Irradiation of hydrated nitroprusside at 77 K is shown to produce two new reduced species. These are both interpreted as the ion [Fe(CN)5NO]3- where the unpaired electron is located in a II* orbital on the nitrosyl group; the difference being only a subtle one involving the geometry of the molecule. The theory of a librating nitrosyl group is proposed to explain their unusual hyperfine parameters. Possible mechanisms of radiation-damage in the anhydrous and hydrated systems are discussed. An infra-red study on the pentacyanonitrosyl ohromate (I) and manganato (I) ions, doped into alkali halido Inttioos, showed a largo number of lines in the nitrosyl stretching region of the spectrum, which were interpreted in terms of the N-0 group interacting with two cation vacancies in the lattice. Infra-red spectra provide strong evidence to show that both complexes are reduced to the zero oxidation state on irradiation of the doped halides. However, an e.s.r. study on irradiated, manganese-doped halides shows the formation of several new paramagnetic species; the complexity of the spectra being such that the expected manganese (O) complex could not be positively identified. Part II deals with the stabilisation of inorganic radicals in precipitated powders. Hydrogen atoms produced in irradiated barium sulphate are shown to interact with neighbouring, impurity sodium ions, hydrogen atoms, formed in other solid matrices, are also shown to be interacting with a second magnetic nucleus. There is also experimental evidence for the formation of the radical-ions H2- and H2+. Finally, we report the formation of the 33 valence-electron C1042- radical in barium sulphate and compare its spectral parameters and geometry with those of isoelectronic species.