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O. Diwald, M. Sterrer, E. Knözinger:
"Site selective hydroxylation of the MgO surface";
Physical Chemistry Chemical Physics, 4 (2002), 2811 - 2817.

On the surface of MgO nanoparticles 1- and multiple (n=3 and 4) coordinated hydroxyl groups are generated site-selectively and studied by transmission infrared spectroscopy. Their formation is
based either on the stepwise dehydration of previously hydrated samples or on simple surface reactions involving molecular hydrogen on one hand, and molecular oxygen, nitrous oxide or properly selected UV quanta on the other as reactants. 4-coordinated OH groups may interact (a)with adjacent surface adsorbats such as hydrides (Mg2+H-) or superoxide anions (Mg2+...O2-)and (b) with surface defects like oxygen anions on steps (O2-) or paramagnetic surface colour centers. In each case the frequency of the respective IR-active OH stretching vibration is indicative of a specific local surface environment to which the OH probe is exposed. On the other hand, only perfectly free and isolated 3-coordinated OH groups have so far been observed. For sterical reasons they are exempt from any interaction with adjacent surface groups or surface defects.

http://pubs.rsc.org/ej/CP/2002/b110334b.pdf