Showing papers by "Fritz Haber Institute of the Max Planck Society published in 1981"

Neutron Propagation in Moving Matter: The Fizeau Experiment with Massive Particles

Abstract: Using a two-slit neutron interferometer, we have measured the shift of the interference pattern induced by the motion of a quartz rod. The measured shift is found to be in agreement with the quantum mechanical prediction derived from a relativity argument. Some peculiarities of the case of massive particles as compared with the classic Fizeau photon case are discussed.

Surface Enhanced Raman Scattering from Pyridine, Water, and Halide Ions on Au, Ag, and Cu Electrodes

Abstract: The enhancement of Raman scattering for pyridine molecules on Au, Ag, and Cu and for water and halide ions on Ag and Cu electrodes has been investigated. — An enhancement has been found only in that spectral region where relative undamped surface plasmon polaritons (SPP) can be excited, showing a general increase for long wavelength excitation. — The electrochemical pretreatment of the metal surfaces. consisting in an oxidation/reduction cycle creates large scale roughness and adatom-adsorbate complexes, both of which are necessary simultaneously in order to obtain intense SER scattering. — It is infered that the enhancement results from high density of SPP quanta created at rough or particularly shaped metal surfaces and the SPP scattering cross section being significant larger than that of photons.

Photoemission study of matrix isolated Cu atoms and clusters

Abstract: Ultraviolet photoemission spectra of Cu atoms and clusters isolated at 7 K in Ar, Kr, and Xe matrices have been measured using He I and He II radiation. For single matrix‐isolated Cu atoms, d‐level emission around 5.1 eV below EF (9.3 eV below Evac) has been observed in all three matrices. Comparison with respective gas phase data yields a relaxation shift (for the 3d94s1 final state) of about 1.3 eV. For matrix‐isolated Cu clusters the emission peak due to d‐band emission is independent of the matrix gas, indicating that the relaxation is solely determined by the cluster itself, rather than by the surrounding matrix. In the matrices doped with clusters the emission from the np levels of the noble gas atoms is markedly modified by the dopant. It is shown that the relaxation of the np levels is dominated by the Cu clusters, yielding emission spectra similar to those from physisorbed noble gases.

New catalysts for the oxidative polymerization of 2,6‐dimethylphenol, 4. The crystal and molecular structure of tetrakis(tetrabutylammonium) hexakis(2,2‐dicyano‐1,1‐ethenedithiolato)octacuprate(i), tetrakis(tetrabutylammonium) hexakis‐(1,2‐dicyano‐1,2‐ethenedithiolato)octacuprate(i), and hexakis[copper(i)‐n,n‐diethylthiocarbamate]

Abstract: The X-ray determination of the crystal structures shows that the dicyanoethenedithiolatocopper(I) complexes [N(C4H9)4]4[Cu8(S2CC(CN)2)6] (1) and [N(C4H9)4]4[Cu8(S(CN)CC(CN)S)6] (2) contain cube-shaped Cu8-clusters, whereas the Cu(I)-N,N-(diethyl)thiocarbamate complex (3) contains a Cu6-octahedron in its centre. A common feature of the three complexes is the coordination of each copper atom by three donor atoms having suitable empty orbitals for back-donation. This results in flat pyramidal arrangements with the basal plane of the three donor atoms being outside the cluster. All clusters deviate significantly from their ideal symmetry. In complex 2 the Cu8-cube is tetragonally elongated and the CuCu-distances are in general much larger (3,20 and 3,70 A, respectively) than in other comparable complexes. Moreover, its anions are fitted into cages of a pseudocubic hydrophobic matrix formed by the tetrabutylammonium cations. It is concluded that is is the bonding within the coordination pyramids of the copper atoms which stabilizes the clusters, whereas the bonding within the clusters seems to be of comparably small importance.

Zero-phonon structures in the optical spectra of some transition-metal ions in CdSe crystals

Abstract: Zero-phonon structures of the ${\mathrm{Fe}}^{2+}$ $3{d}^{6}^{5}E(D)\ensuremath{\leftrightarrow}^{5}T_{2}(D)$ transition in absorption and emission include a coinciding line at 2376 ${\mathrm{cm}}^{\ensuremath{-}1}$. Polarized transmission spectra of the ${\mathrm{Co}}^{2+}$ $3{d}^{7}$ transition $^{4}A_{2}(F)\ensuremath{\rightarrow}^{4}T_{1}(P)$ display components split by second-order spin-orbit coupling and indicate an autoionization effect at the 14 175-${\mathrm{cm}}^{\ensuremath{-}1}$ line. Symmetry arguments support the interpretation of this antiresonance by a ${\mathrm{Co}}^{2+}\ensuremath{\rightarrow}{\mathrm{Co}}^{3+}$ charge-transfer process with a threshold at about 13 800 ${\mathrm{cm}}^{\ensuremath{-}1}$. The $^{4}T_{2}(F)\ensuremath{\rightarrow}^{4}A_{2}(F)$ luminescence transition of ${\mathrm{Co}}^{2+}$ gives rise to a zero-phonon line at 2867 ${\mathrm{cm}}^{\ensuremath{-}1}$. The fine structure of the $^{3}T_{1}(F)\ensuremath{\rightarrow}^{3}T_{1}(P)$ absorption of ${\mathrm{Ni}}^{2+}$ $3{d}^{8}$ suggests a strong reduction of spin-orbit coupling by the Jahn-Teller interaction. With ${\mathrm{Ni}}^{2+}$ ions, radiative recombination from the $^{3}T_{1}(P)$, $^{3}A_{2}(F)$, and $^{3}T_{2}(F)$ levels to the $^{3}T_{1}$ ground state is detected, and the first and the last transitions exhibit zero-phonon lines at 10 926 and 3607 ${\mathrm{cm}}^{\ensuremath{-}1}$, respectively. An abundant novel emission band characterized by a zero-phonon transition at 10 170 ${\mathrm{cm}}^{\ensuremath{-}1}$ may be related to an $M$ center, i.e., a ${({V}_{\mathrm{Se}}^{\ensuremath{-}}{V}_{\mathrm{Se}}^{\ensuremath{-}})}^{2+}$ associated defect.