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The electron transfer rate between tetracyanoquinodimethane and its radical anion is measured for different solvents and temperatures using ESR line broadening. The solvent polarity term γ = 1/n2 - 1/ε (n is the refractive index, ε the dielectric constant) could be changed in the range 0.05 ≤ γ ≤ 0.53. The true rate constants k (corrected for diffusion) are discussud in terms of the classical theory of electron transfer. A linear dependence of ln k on γ is only found with a viscosity-dependent pre-exponential factor. The outer reorganization energy is small compared with the inner and has a negative sign. This is explained by the special arrangement of the ellipsoidal reactants in the activated complex. 相似文献
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Roswitha Harrer 《Chemie in Unserer Zeit》2010,44(5):316-317
Die Entwicklung der künstlichen Photosynthese und somit die mehr oder minder direkte Nutzung der Sonnenenergie ist seit Jahren ein zentrales Thema. Wie kann man Sonnenenergie billiger und besser zugänglich machen? Konkrete Empfehlungen für die zukünftige Forschung sprechen Wissenschaftler nach dem ersten Chemical Sciences and Society Symposium (CS3) zur Nutzung von Sonnenlicht aus. 相似文献
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The Feynman path integral Monte Carlo approach has been coupled to the gauge including atomic orbital formalism in order to analyse the absolute magnetic shieldings of the benzene nuclei under the conditions of thermal equilibrium. The Hamiltonian employed in the derivation of ensemble averaged NMR quantities is of the Hartree-Fock type. The basis set used is of 6–31G quality. The spatial delocalization of the atoms leads to a deshielding of both types of benzene nuclei relative to the shieldings experienced at the minimum of the potential energy surface. This deshielding has to be traced back to bond length elongations in thermal equilibrium. The influence of the nuclear fluctuations on the NMR parameters of benzene is quantum driven up to temperatures of 400 K; classical fluctuations are of minor importance in this low-temperature window. 相似文献
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Eva Marie Freiberger Dr. Julien Steffen Natalie J. Waleska-Wellnhofer Anton Harrer Felix Hemauer Valentin Schwaab Prof. Dr. Andreas Görling Prof. Dr. Hans-Peter Steinrück Prof. Dr. Christian Papp 《Chemphyschem》2023,24(22):e202300510
This study addresses a fundamental question in surface science: the adsorption of halogens on metal surfaces. Using synchrotron radiation-based high-resolution X-ray photoelectron spectroscopy (XPS), temperature-programmed XPS, low-energy electron diffraction (LEED) and density functional theory (DFT) calculations, we investigated the adsorption and thermal stability of bromine on Rh(111) in detail. The adsorption of elemental bromine on Rh(111) at 170 K was followed in situ by XPS in the Br 3d region, revealing two individual, coverage-dependent species, which we assign to fcc hollow- and bridge-bound atomic bromine. In addition, we find a significant shift in binding energy upon increasing coverage due to adsorbate-adsorbate interactions. Subsequent heating shows a high thermal stability of bromine on Rh(111) up to above 1000 K, indicating strong covalent bonding. To complement the XPS data, LEED was used to study the long-range order of bromine on Rh(111): we observe a (√3×√3)R30° structure for low coverages (≤0.33 ML) and a star-shaped compression structure for higher coverages (0.33–0.43 ML). Combining LEED and DFT calculations, we were able to visualize bromine adsorption on Rh(111) in real space for varying coverages. 相似文献
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Roswitha Harrer 《Chemie in Unserer Zeit》2004,38(4):227-227
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