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Spectroscopic Properties of Trapped Electrons on the Surface of MgO Nanoparticles
Author(s) -
Sterrer Martin,
Berger Thomas,
Stankic Slavica,
Diwald Oliver,
Knözinger Erich
Publication year - 2004
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200400266
Subject(s) - electron paramagnetic resonance , chemistry , unpaired electron , electron , heterolysis , crystallography , nuclear magnetic resonance , physics , quantum mechanics , catalysis , biochemistry
To characterise electron‐trapping sites on the surface of MgO nanoparticles, surface colour centres were generated using UV light in conjunction with selected hydrogen‐based electron sources. Four different colour‐centre species, including the characteristic (e − )(H + ) or F ${{{+\hfill \atop S\hfill}}}$ (H) centre, were identified due to the distinct shape of the respective electron paramagnetic resonance (EPR) signals. The analysis of the EPR saturation behaviour down to microwave powers of 5×10 −3 mW reveals an enhanced spin‐relaxation probability of the (e − )(H + ) centre compared to all other F ${{{+\hfill \atop S\hfill}}}$ centres that do not exhibit significant magnetic interactions with hydroxylic protons. Beside the dipolar magnetic interaction in the (e − )(H + ) centre observed by EPR, the electronic interaction between the unpaired electron and the proton of a closely spaced OH group produces a redshift of the OH stretching band by about 70 to 170 cm −1 , as observed by infrared spectroscopy. EPR and IR spectroscopic data obtained after the selective address of individual reaction channels for surface colour‐centre formation point to the fact that (e − )(H + ) centres are formed by trapping electrons from H atoms. Consequently, the underlying surface defect does not belong to the sites of the MgO surface, which chemisorb hydrogen via a heterolytic splitting process.