Lumineszenzspektren von ein- und zweikernigen Chrom(III)-Glycin-Komplexverbindungen

The luminescence spectra of the polycrystalline compounds [Cr(CH₂NH₂COO)₃ · H₂O] and [Cr₂(OH)₂(CH₂NH₂COO)₄] are investigated in the temperature range of 120K – 4.2K. From the known crystal structure (P2_1/c =D _2h ^/5 ) of the mononuclear compound assignment of the zero-phonon bands based on crystal field theory becomes possible. Both of the highly intense phosphorescence transitions are observed at \(P_1 = 14493 cm^{ - 1} ({}^2A'' \xrightarrow{{0.0}} {}^4A) and P_2 = 14428 cm^{ - 1} ({}^2A' \xrightarrow{{0.0}} {}^4A)\) . Assignment of the accompanying vibronic bands is made from the measured infrared data. Crystal field parameters Dq, B and C are determined from the luminescence and reflectance spectra. In the case of the binuclear compound the Cr³⁺-Cr³⁺ interaction via hydroxyl brides may be described by an axchange operator \(H_{ex} = - 2 \sum\limits_{ij} {J_{ij} S_i^a \cdot S_j^a } \) and from this the energy level diagram is calculated. Both observed strong phosphorescence bands at 14369 cm^?1 and 14184 cm^?1 are assigned to \(\left| {{}^2E \cdot {}^4A_2 \rangle _{s = 2} \xrightarrow{{0.0}}} \right| {}^4A_2 \cdot {}^4A_2 \rangle _{s = 2} and \left| {{}^2E \cdot {}^4A_2 \rangle _{s = 1} \xrightarrow{{0.0}}} \right| {}^4A_2 \cdot {}^4A_2 \rangle _{s = 1} \) transitions.     

Guest-host interaction and photochemical transformation of silver particles isolated in rare gas matrices

Silver dimers and small clusters isolated in rare gas matrices are studied by UV-VIS absorption, emission, and resonance Raman spectroscopy. One, two, and three dimer trapping sites can be identified in Xe, Kr, and Ar matrices, respectively. The sites are identified by computer simulation to be either ofD _4h symmetry, with the molecules aligned in the 〈100〉-direction of thefcc-host lattice, or ofD _2h symmetry, with the molecules occupying single or double vacancies and aligned in the 〈110〉-direction. Low energy external modes of the dimers are observed in the resonance Raman spectra. They probe the guest-host interaction of the molecules and are assigned to librational modes. Trimers and larger clusters are found to be very photosensitive. Three different trimers can be observed in Xe and Kr matrices, respectively. They can be transformed reversibly into each other by laser irradiation. This indicates that probably three corresponding isomers can get stabilized in the two matrices. Further evidence for this interpretation is obtained from emission spectroscopy. Despite the photosensitivity of the trimers it is possible to stabilize the concentration of a particular species by a dual beam technique. Thus we obtained a resonance Raman spectrum of one species in a Xe matrix and a preresonance spectrum of the corresponding species in a Kr matrix.     

Untersuchungen über das Vorkommen von Eiweiss in der pflanzlichen Zellhaut,nebst Bemerkungen über den mikrochemischen Nachweis der Eiweisskörper

Ohne ZusammenfassungVorliegende Abhandlung bildet den chemischen Theil einer pflanzen-physiologischen Arbeit, welche vollständig in den Sitzungsber. der kais. Akad. d. Wiss., XCIV. Bd., I. Abth., December 1886 erscheinen wird.     

Enhanced raman scattering from small metallic particles and Metallic Films

Summary We report surface enhanced Raman scattering of benzene adsorbed on nickel and platinum particles and on cold evaporated copper films. The vibrational bands of benzene are only slightly shifted with respect to solid benzene. Additional bands are found, which are symmetry forbidden in the free benzene molecule. These bands result from the low site symmetry of the molecule at the surface. The Raman enhancement depends strongly on the size and shape of the metal particles involved. To better understand this geometrical dependence, we made up a program to study the interaction of small metal clusters with adsorbed molecules. Some preliminary results obtained with matrix isolated copper clusters are reported.

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Verstärkte Ramanstreuung an kleinen Metallteilchen und Metallfilmen

Zusammenfassung Es wurde der oberflächenverstärkte Ramaneffekt von Benzol adsorbiert auf katalytischen Nickel- und Platinteilchen und von kalt aufgedampften Kupferfilmen untersucht. Die Schwingungsbanden von Benzol sind nur unwesentlich verschoben verglichen mit festem Benzol. Es wurden zusätzliche Schwingungsbanden gefunden, die im freien Benzol symmetrieverboten sind. Diese Banden resultieren von der niedrigen Mikrosymmetrie des Moleküls auf der Oberfläche. Die Ramanverstärkung ist stark abhängig von Größe und Form der Metallteilchen. Um ein besseres Verständnis der Abhängigkeit von geometrischen Faktoren zu erlangen, haben wir damit begonnen, die optischen Eigenschaften kleiner Teilchen und ihre Wechselwirkung mit adsorbierten Molekülen zu studieren. Es werden erste Ergebnisse von matrixisolierten Kupferclustern diskutiert.

     

Brillouin scattering in cubic potassium cyanide

The temperature dependence of the elastic shear constant C₄₄ of cubic potassium cyanide has been measured by optical Brillouin spectroscopy in the temperature range from 300-168 K. A strong softening of the constant C₄₄ was found in agreement with the results of ultrasonic and neutron measurements.     

Enhanced raman spectra of molecules adsorbed on small metal particles

The Raman spectra of benzene adsorbed on small nickel and platinum particles have been measured. The spectra are strongly enhanced, compared with those wavelengths, where no enhancement has been observed. The spectra of benzene adsorbed on platinum and nickel particles are rather similar. The most intensive vibrational band is the totally symmetric breathing mode, which dominates the spectrum. Besides the Raman active vibrations, some other weak vibrational modes are observed, which may be assigned to normally infrared and inactive vibrational transitions. The enhanced Raman effect seems to be dependent on the particle size and shape. Therefore it is important to investigate the behaviour of small metallic particles. First results of pyridine bonded to Ag₂ and Ag₃ are reported.     

Population dynamics of the two light induced metastable states in Na2[Fe(CN)5NO]·2H2O single crystals

The dependence of the population dynamics on intensity, time, wavelength and polarisation of the illuminating light and on the temperature of both metastable states in Na₂ [Fe(CN)₅NO]·2H₂O single crystals is investigated by differential scanning calorimetry. The population and depopulation behaviour can be described by exponential functions. The wavelength dependence shows the spectral range in which both states can be excited and the existence of a transfer process from state II into state I. Further, light of the near infrared region, transfers state I into state II.     

Pseudo-Simplicial Complexes from Maximal Locally Convex Functions

We introduce and discuss pseudo-simplicial complexes in ℝ^d as generalizations of pseudo-triangulations in ℝ². Our approach is based on the concept of maximal locally convex functions on polytopal domains.     

Investigation of the metastable state of Na2[Fe(CN)5NO] · 2H2O by optical spectroscopy. II The electronic spectra of the ground and metastable states

The absorption spectra of Na₂[Fe(CN)₅NO] · 2H₂O were measured in the visible region in the range of 3400–7000 Å. In the metastable state, an additional absorption band in the long wavelength range is observed and the transition $\text{2}\text{b}{}_{\mathrm{<mtext>2</mtext>}}\text{(d}{}_{\mathrm{xy}}\text{)→}\text{7}\text{e(π}{}^1\text{?NO}\text{)}$ becomes weaker in the excited state indicating a population of the π¹(NO)-orbital. The laser excited emission spectrum shows a broad luminescence beginning at the excitation line $\text{λ =}\text{5145}\text{A}\text{?}\text{(}\text{19,436 cm}{}^{-1}\text{)}$ with a maximum at about 6250 Å (16,000 cm^-1). A strong sharp luminescence at about 7836 Å is registered and may be assigned to a transition 3b₁(d_x²?y²) or 5a₁(d_z²) to the antibonding π¹(NO)- orbital. Further the broad luminescence is superimposed by a series of sharp spikes. These sharp spikes can also be observed for several days, when the laser is switched off, and are depending on the crystal orientation.     

Resonance Raman scattering by localized and resonant modes of Ag2 molecules in rare gas matrices

We demonstrate for the first time that excitation of silver containing rare gas matrices at 406.74 nm results in resonance Raman spectra which show low energy localized and resonant modes. As they combine with the Ag₂ stretching vibration and its overtones, they can unambiguously be attributed to the Ag₂ molecule. In Xe-matrices the coupling of lattice phonons and impurity vibrations is documented by side bands which resemble the phonon density of states of the host lattice. Two trapping sites are observed in Kr-matrices.