The adsorption isotherm of H2O has been measured on three kinds of MgO, and the bulk rehydration has been found to occur at a moderate pressure range of H2O, which exhibits a break in the isotherm. Infrared studies show that the surface hydration gives an isolated absorption peak at 3730 cm-1 due to free OH and a broad band centred at 3550 cm-1 due to hydrogen-bonded OH, whereas the bulk hydration exhibits a new absorption peak at 3695 cm-1. On evacuation, the bulk OH can be dehydrated at temperatures lower than those of the surface free OH. The exchange reaction of all kinds of OH with D2O was found to be slow. The initial bulk hydration necessitates a higher vapour pressure of ca. 4-6 Torr, but 3.5 Torr D2O is sufficient for the deuteration of bulk OH once formed. The successive exposure of the sample, having been subjected to the initial bulk hydration with H2O, to 10 Torr D2O causes an additional bulk hydration with D2O after a semi-complete surface deuteration, and gives rise to an increase in the peak intensities of lower-frequency bands in the OH stretching region.
|Number of pages||10|
|Journal||Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases|
|Publication status||Published - Dec 1 1988|
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