Applications of electron spin echo envelope modulation spectroscopy to catalytic systems

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1992

OSTI ID:5649626

Cosgrove, S A

ESEEM (electron spin echo envelope modulation) spectroscopy is applied to adsorbed species on dispersed catalytic systems. Measurements of electron-nuclear spin coupling constants, specifically and nuclear hyperfine and quadrupole coupling constants, and their subsequent interpretation, provide site-specific, structural information about nuclei in the vicinity of the paramagnetic center. This information is useful in elucidating the chemical identity and structural environment of the adsorbed species. Spectroscopic techniques, such as multifrequency and orientation-selective ESEEM, are utilized to exploit the external field strength dependences of spectral features, in order to facilitate the assignment of peaks and the determination of coupling constants. A multifrequency ESEEM study of m-dinitrobenzene radicals formed by interfacial electron transfer from a [gamma]-alumina surface yields the isotropic hyperfine and quadrupole coupling constants for the weakly coupled nitrogen. Based on these results, the surface species is identified as an ion-pair. The impact of hyperfine anisotropy on [sup 14]N ESEEM patterns is assessed using perturbation theory and numerical simulations. Ammonia adsorption on silica supported vanadium surfaces is examined via multifrequency and orientation-selective ESEEM spectroscopy. The hyperfine coupling constants for nitrogen suggest coordination of the ammonia cis to the vanadyl bond, and the quadrupole coupling constants imply near axial symmetry of the electric field gradient at the nitrogen. Similar results are obtained for a related catalytic system of ammonia adsorbed on silica supported molybdenum. The validity of the high field approximation is examined and verified when the electron excitation frequency is at least an order of magnitude larger than the characteristic nuclear frequencies.

• Research Organization: Harvard Univ., Cambridge, MA (United States)
• OSTI ID: 5649626
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400102 -- Chemical & Spectral Procedures
400201* -- Chemical & Physicochemical Properties
ADSORPTION
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
AMMONIA
ANISOTROPY
AXIAL SYMMETRY
CATALYST SUPPORTS
CATALYSTS
CHALCOGENIDES
COUPLING CONSTANTS
ELECTRON TRANSFER
ELEMENTS
HYDRIDES
HYDROGEN COMPOUNDS
MATHEMATICAL MODELS
METALS
MINERALS
MOLYBDENUM
NITRO COMPOUNDS
NITROBENZENE
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PERTURBATION THEORY
RADICALS
SILICA
SILICON COMPOUNDS
SILICON OXIDES
SORPTION
SORPTIVE PROPERTIES
SPIN ECHO
SURFACE PROPERTIES
SYMMETRY
TRANSITION ELEMENTS
VANADIUM