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The system di-tert-butyl nitroxide (DTBN) adsorbed on a thin film of γ-Al 2 O 3 (111) grown on a NiAl(110) single crystal has been studied with various surface science methods, including TPD, XPS, NEXAFS, and ESR line-shapes analysis. In the monolayer regime, two strong chemisorbed species with adsorption energies of 120 and 150 kJ/mol, respectively, are found after adsorption at 40 K. One species is ESR active and reveals distinct dynamic behavior above 200 K through cw ESR line-shape analysis. The second species is oriented with an angle of about 70°between the surface normal and the N-O axis of the molecule, as the NEXAFS data show. Missing of the π* resonance and the ESR inactivity suggest a direct participation of the half-filled π* orbital located at the nitrogen atom in the bonding mechanism. Above 200 K, both adsorbed species exchange with each other. This could be followed by monitoring the temperature-dependent ESR intensity. Adsorption at room temperature leads to the formation of a third unstable species which is ESR active but shows a different ESR spectrum in comparison with the other ESR-active species. The accessibility of the nitrogen atom for bonding is discussed on the basis of high-quality ab initio calculations.

The adsorption of NO2/ads on a clean Au(111) surface has been studied using electron spin resonance (ESR) and thermal programmed desorption (TPD). NO2/Au(111) appears to be an appropriate system in which to detect an ESR signal, because it is known from the literature that NO2 adsorbs as a molecule and is bonded through its oxygen atoms to the surface, while the spin is more localized at the nitrogen atom. In agreement with former results, no resonance of a paramagnetic monolayer on a clean single-crystal metal surface is observed. However, a well resolved spectrum from a multilayer has been detected. Orientation of the molecules in the multilayer has been studied via angle-dependent measurements in combination with computer simulation. Temperature-dependent measurements are used to investigate reactivity and molecular motion.

The molecular dynamics of one monolayer adsorption species of di-tert-butyl nitroxide (DTBN) adsorbed on a thin film of γ-Al 2 O 3 (111) grown on a NiAl(110) single crystal has been studied via ESR line-shape analysis. Below 200 K a rigid limit spectrum is found, above this temperature the changes in line shape are consistent with slow motions of the molecule. Best agreement between the experimental spectra and simulations is obtained using a "moderate jump" model with both Brownian diffusion and jump type contributions to the molecular dynamics. The motional processes have an activation energy of about 9 kJ/mol.

We report on the first electron spin resonance (ESR) investigation of the molecular rotational motion of self-assembled monolayers. We present results on fatty acid films grown on a thin Al2O3 film. The spectra reveal a distinct temperature and coverage dependence. The changes in the line shape with variation of the spin labels location along the alkyl chain allow insight into the internal dynamics of self-assembled films.