Electronic spectra of carotenoids. Schiff's bases of carotenal and carotenones

Visible absorption bands of β-apo-8′-carotenal, citranaxanthin, and reticulataxanthin Schiff's bases are measured and analyzed in relation to the visual chromophore, retinal Schiff's base. The former shows a strong red shift of the absorption maxima upon protonation in ethanol, and the magnitude of the band shift is comparable to that of retinal Schiff's base. Molecular orbital analysis of the ground and excited state electronic structures of both types of Schiff's bases suggests the usefulness of carotenal Schiff's bases as a model for comparative studies with visual chromophore.     

Effect of temperature on surface composition of Cu-Sn and Ag-Sn alloys; an ESCA study

Cu-Sn and Ag-Sn alloys containing 5% Sn were studied by ESCA. The heats of surface segregation of Sn obtained from equilibrium measurements of the surface composition as a function of temperature were found to be 12.0 ± 1.0 and 3.5 ± 1.0 kcal/mol for Cu-Sn and Ag-Sn alloys, respectively. These results are compared with the predictions of existing theories. Possible reasons for the difference between the experimental result and theoretical prediction are also discussed.     

A study of dilute tin alloys by x-ray photoelectron spectroscopy

X-ray photoelectron spectra of Pb₉₈Sn₂, Ag₉₅Sn₅, Sb₉₅Sn₅ and Cd_99.6Sn_0.4 have been recorded using a VG Scientific ESCA-3 Mk. II electron spectrometer. In all cases the Sn 3d level in the alloys is compared with the 3d level in pure tin. The binding energy shifts are explained on the basis of electronegativity and near-neighbour interactions. It is found that increased coordination number as well as increased electronegativity of the neighbouring atoms increases the binding energy of the core electron level.     

High resolution infrared spectrum of CH3Br: The ν4 band near 3100 cm−1

A Fourier transform spectrum (resolution 0.005 cm^?1) of the ν₄ band of methyl bromide has been analyzed. More than one thousand lines have been assigned for each isotopic species CH₃⁷⁹Br and CH₃⁸¹Br. A perturbation is apparent mainly near KΔK = 5. It was interpreted as due to a Coriolis interaction with ν₃ + ν₅ + ν₆. The whole spectrum is reproduced with a standard deviation smaller than 10^?3 cm^?1. Finally, the “hot” band ν₄ + ν₃ ? ν₃ has been assigned and analyzed.     

Optical spin orientation in ruby by Zeeman-selective U-band absorption

Optically induced magnetization in ruby at room temperature has been observed by excitation of the U-absorption band. Optically induced Zeeman coherence associated with different pairs of Zeeman sublevels has also been observed as free induction decay signals. Zeeman-selectivity in the U-band transition is derived by assuming a spin-orbit coupling which provides a small fraction of the intensity of the U-band. Calculation of the relative transition probability yields different Zeeman population distributions depending on the types of irreducible representations used for the spin-orbit coupling.     

The He(I) photoelectron spectra of BrF and IF

The vacuum ultraviolet photoelectron spectra of BrF (X¹Σ⁺) and IF (X¹ Σ⁺) have been recorded and interpreted with the aid of both MS — Xα — SCF calculations and ab initio calculations. For both BrF and IF the first band is split by spin—orbit coupling into two components corresponding to ionization to the X²Π$\text{3}\text{2}$ Phytochemistry and X²Π$\text{1}\text{2}$ ionic states. Estimates of re, ?we and De for these states have been made.     

Epr studies of some arsenic and phosphorus oxyradicals

EPR studies of radicals such as AsO₃^2, AS0₄^2, [AsO₄…PO₄]^5 and PO₄^2 produced in mixed arsenate-phosphates by radiation damage are described. These radicals are stable in these impure systems and their magnetic parameters are correlated with the crystallographic structure of the respective host-lattices.     

Fluorescence ratio of the two D sodium lines in flames for D1 and D2 excitation

The ratio of the fluorescence intensities from the two lines of the yellow sodium doublet has been investigated in several hydrogen-based and acetylene-based flames and with various types of lasers as excitation sources. The systematic deviation from 2 for the ratio D₂/D₁ when either D₁ or D₂ are used as exciting transitions can be simply explained by the relative difference in the values of the collisional mixing constants between the excited P-levels and the collisional quenching constants transferring atoms from both P-levels to the ground S-level. Results obtained in flames characterized by different values of the quantum efficiency follow the behavior predicted by the fluorescence expressions obtained by a simple, steady-state theoretical approach.     

Mössbauer studies on cation distribution and lattice distortion in magnesium manganites

Mössbauer studies are reported on a magnesium manganite series Mg_xMn_2.9?xFe_0.1O₄ for 0.5 ? x ? 2.4. In the region x ? 1.4 two quadrupole doublets are observed while for x ? 1.8 only one doublet could be observed. Quadrupole splitting (QS) has been studied as a function of x and an unusually large QS for the outer doublet has been attributed to Jahn-Teller distortion whose onset has been located in the region 1.8 > x > 1.4; this is corroborated by X-ray diffraction studies. Probable cation distributions are proposed. Oxygen ion parameters are estimated for the compositions corresponding to x = 1 (tetragonal phase) and x = 2 (cubic phase) under point charge approximation for electric field gradient at Fe³⁺ sites.     

Heavy-atom effect on radiative and radiationless transitions in charge-transfer complexes

The quantum yields of fluorescence and phosphorescence and decay times of fluorescence were measured for a series of charge-transfer complexes of hexamethylbenzene (an electron donor) with various electron acceptors containing heavy (halogen) atoms and the rate constants of different radiative and radiationless transitions were determined. It was found that radiative T₁ → S₀ transition, i.e. the phosphorescence, is strongly enhanced by the heavy-atom effect. The mechanism of the heavy-atom enhancement of charge-transfer phosphorescence is discussed and it is concluded that increasing spin- orbit mixing of radiative T₁ → S₀ charge-transfer transition with singlet-singlet, locally excited transition of acceptor molecule is responsible for the observed effects.     

Mössbauer studies on cation distribution and lattice distortion in magnesium manganites — II

Mössbauer studies are reported on a magnesium manganite series Mg_xMn_2.9?xFe_0.1O₄ (0.5?x?2.4) obtained by quick quenching (in water at 300 K) after heat treatment of the stoichiometric oxide mixtures. The data on quadrupole splitting have been interpreted in terms of Jahn- Teller distortion due to high spin Mn³⁺ ions occupying octahedral sites. Detailed analysis suggests that the cations distribute in a partially inverse configuration as against a normal one in the case of the series obtained by slow cooling of the mixtures after their heat treatment, reported in a previous communication.     

XPES studies of oxides of second- and third-row transition metals including rare earths

X-ray photoelectron spectroscopy has been employed to investigate oxides of second- and third-row transition metals, including those of rare earths. Systematics in the spin—orbit splittings and binding energies of core levels of the metals are described. In most of the cases studied, the dependence of the spin—orbit splittings on the atomic number Z is given by the relation ΔE = a(Z - Z₀)⁴, where a is the quantum defect parameter and Z₀ is the effective screening. Core-level binding energies are found to increase with the oxidation state of the metal. Most of the core-level binding energies are related to the atomic number Z by the expression E = x(Z - Z₀)², giving rise to linear plots of ln E versus ln Z. Specific features of individual oxides, with respect to satellites, multiplet structure, configuration mixing, and other properties are also discussed. The spectra of PrO₂, Pr₆O₁₁, TbO₂ and Tb₄O₇ are reported for the first time.     

Effect of chlorine on the adsorption of oxygen on Cu and Ag surfaces

Based on XPS and UVPS studies, it is shown that oxygen is preferentially adsorbed molecularly in the singlet state on Cu and Ag surfaces containing presorbed chlorine. Adsorption of chlorine on Cu and Ag surfaces containing presorbed atomic oxygen causes a disappearance of the oxygen. Extended Hückel calculations predict the observed behaviour.     

An x-ray photoelectron-spectroscopy study of Naβ-alumina surfaces

The cleavage-face of a sodim-β-alumina crystal was studied by means of X-ray photoelectron spectroscopy (XPS). A detailed quantitative analysis, which took into account the particular layered structure in this crystal, revealed a significantly (≈50%) Na deficient surface produced by cleaving the crystal along a conduction plane. The expressions derived for the elemental composition are applicable to any layered structure. Ion sputtering of the cleavage surface caused atom mixing in the layered structure as well as a preferential removal of the mobile sodium ions. Auger electron spectroscopy (AES) measurements showed that unlike the cleavage surface, the edge surface contains a significantly high concentration of sodium.     

Detection of a second Br site in K2Pt(CN)4Br0.3 3.2 H2O (KCP) by 18Br and 39K NMR

By nuclear magnetic resonance we have detected between 20 and 300 K two bromine signals with a temperature-independent intensity ratio of 2.5 ± 0.3 proving the existence of a second Br site in KCP. The result is supported by the observation of three potassium signals. Thus, three types of unit cells exist: 40% contain defect water, 43% have Br in site I and 17% Br in site II.     

Residual entropy of the one-dimensional Ising antiferromagnet with general spin

We have calculated the ground-state degeneracy and the concominant residual entropy of the one-dimensional Ising antiferromagnet in a critical magnetic field. We demonstrate that the results obtained can be related to the ground-state properties of the q-state Potts antiferromagnet in the corresponding external field.     

Electron energy loss and Auger study of epitaxially grown Cu on Ni(100)

Auger and electron energy loss spectra have been measured on films of Cu epitaxially grown on Ni(100). The films were prepared under UHV conditions using a quartz crystal for monitoring the deposition rate. LEED measurements were taken to determine the orientation of the films. The presence of a monolayer of Cu on Ni(100) is enough to suppress the 3p-3d transition on the surface of the sample. The electron energy loss spectra were studied as a function of the primary electron energy (50 to 300 eV). The experimental results were qualitatively analyzed using recent theoretical calculations of Cooper and co-workers. The effect of a small Cu coverage on Ni(100) on the chemisorption of CO and O₂ was also studied. A strong suppression of CO chemisorption at room temperature was observed. In the case of O₂, large exposures are necessary in order to observe a significant amount of oxygen on the surface. The absence of any appreciable chemisorption on the surface of the metal is attributed to the lack of empty d-surface states.     

Measurements of bulk-to-surface segregation of impurities in electrodeposited NiCr alloys by auger electron spectroscopy

Auger Electron Spectroscopy (AES) measurements of the non-equilibrium segregation of K to the surface of an electrodeposited NiCr alloy of 20%Ni-80%Cr composition are reported. It is shown that a surface enrichment of K takes place on the surface to a maximum of 8% coverage in the temperature range 400–550°C. The process is initially diffusion-connrolled, with an activation energy of 17 ± 3 kJ/mol. An electrodeposited alloy of approximately 80%Ni-20%Cr composition showed a considerable C-enrichment at the surface in the temperature range 300 to 600°C. A cast alloy of the same composition showed a similar C-enrichment in the temperature range 300 to 455°C. The electrodeposited alloy of 20%Ni-80%Cr showed no such C-enrichment, due to the segregation of both K and Cr to the surface in the range 300 to 600°C and the formation of chromium carbide precipitates.