Abstract
Oxygen chemisorption at 20°C has been examined in ZnO samples derived by vacuum decomposition of zinc carbonate. Evidence is given that an e.s.r. spectrum with features at g-values of 2.051, 2.042, 2.0085 and 2.0036 results from the super-position of triplet spectra characterized by different low field features at g-values of 2.051 and 2.042. A further signal at g≃ 1.96 also observed prior to chemisorption is assigned to free electrons from donors. Spin density measurements for the chemisorption spectrum and the signal at g≃ 1.96 provide evidence that the two triplet spectra result from different processes. The triplet spectrum with the low field feature at g≃ 2.051 is assigned to O–2 radicals resulting from trapping of free electrons. The other spectrum is attributed to O–2 or O– radicals arising from oxygen interaction with electrons in surface defects. A model is discussed in which the radicals from both processes are adsorbed on cation sites neighbouring an oxygen ion vacancy.
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Schedule a callMore From: Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases
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