Additional Weak Band Research Articles

An UV/Vis/NIR optical absorption spectroscopic and color investigation of transition-metal-doped gahnite (ZnAl2O4 spinel) crystals grown by the flux method

Abstract Synthetic flux-grown end-member gahnite, ZnAl2O4, and several different colored crystals doped with one or more transition metals including Mn, Ni, Cr, Co, and Fe were studied by electron microprobe methods and UV/Vis/NIR single-crystal optical absorption spectroscopy. The first major objective was to measure and assign the various electronic absorption features. The second was to analyze quantitatively the crystal colors using the experimental spectra and the CIE 1931 color-space-chromaticity diagram. The microprobe results show that the doped gahnites have transition metal concentrations between about 0.001 and 0.1 cations per formula unit. The spectrum of colorless, nominally pure ZnAl2O4 displays no absorption in the visible region. Microprobe analysis of a light-blue gahnite crystal reveals small amounts of Ni and Mn. The UV/Vis/NIR spectrum does not indicate any dd-electronic transitions relating to Mn. All absorption features also cannot be fully interpreted using Tanabe-Sugano diagrams for Ni2+ in either octahedral or tetrahedral coordination. A series of seven slightly different colored gahnites with differing concentrations of Cr3+ and most also containing smaller amounts of Ni was investigated. The spectrum of a one pink crystal shows two intense absorption features in the visible region. They are assigned to spin-allowed 4A2g → 4T2g (4F) and 4A2g → 4T1g (4F) transitions of VICr3+. Other spectra display additional weak bands and lines that are most probably spin-forbidden dd-transitions of Ni2+. These gahnites with Ni and Cr show varying purple colorations depending on the concentrations of both metals. Two more deeply blue gahnites contain Co2+ as demonstrated by their UV/Vis spectra but not by microprobe analysis. Two intense absorption features at ~7440 and ~16 850 cm–1 are observed and assigned to the spin-allowed transitions 4A2 → 4T1 (4F) and 4A2 → 4T1 (4P) of Co2+, respectively. Complex absorption fine structure, caused by spin-orbit and/or vibronic interactions, is also observed. Three different gahnites with yellow to orange colorations contain measurable Mn. Their spectra are similar in appearance and display several weak IVMn2+ spin-forbidden transitions located above 20 000 cm–1. The spectra of two green gahnites show several Fe spin-forbidden electronic transitions arising from single, isolated IVFe2+ and VIFe3+ cations between 10 000 and 25 000 cm–1. The intensities of some of the VIFe3+-related bands can be increased through exchange-coupled interactions with next nearest IVFe2+ neighbors. The colors of various doped gahnites and the end-member galaxite are analyzed using their single-crystal absorption spectra in the visible region. Their dominant wavelength, λk, and hue saturation, pc, values are given on the CIE 1931 color-space-chromaticity diagram and are discussed. The Hex colors of all crystals are calculated and can be compared to those of the studied crystals.

Mixed ionic–electronic effect on up–conversion in Er3+/V4+ co–doped Na2O–CaO–B2O3 glasses with enhanced red emission

Optical absorption and emission properties of 20Na2O–20CaO–(59 – x)B2O3–xV2O5–1Er2O3 (x = 0 – 2.5 mol%) (Series A) and 20Na2O–20CaO–(58.5 – y)B2O3–1.5V2O5–yEr2O3 (y = 0 – 3.0 mol%) (Series B) glass systems were examined to elucidate the effect of Er2O3 co–doping with V2O5 in the mixed ionic–electronic (MIE) glasses. The absorption spectra of both glass series exhibited 10 significant bands, which corresponded to the f–f transition of Er3+ ions with an additional weak absorption band attributed to V4+ energy transition. The up–conversion PL spectra for the glasses under 779 nm excitation displayed 3 emissions bands centered at 518, 556 and 647 nm due to the emission from the energy levels of Er3+. The enhanced emission at 647 nm (red region) that corresponded to the 4F9/2 → 4I15/2 of the Er3+ transition for all glasses was suggested due to energy transfer from V4+ to Er3+ ions. For Series A, the variation of oscillator strength (fexp) and Judd–Ofelt parameters (Ω2,4,6) showed almost similar trend, which exhibit a maximum at x = 0.5 mol% V2O5. PL intensity was highest for sample x = 0.5 mol% but abruptly drops to the minimum at x = 1.5 mol%. The decrease in PL was possibly influenced by the MIE effect. Meanwhile, for Series B glasses, general decrease was observed in fexp and Judd–Ofelt parameters except for Ω6 upon Er2O3 addition. The PL intensity increased and reached a maximum at y = 2.0 mol% before subsequently decreased with further addition of Er2O3 (y = 3.0 mol%) due to concentration quenching.

Optical Absorption of Excimer Laser‐Induced Dichlorine Monoxide in Silica Glass and Excitation of Singlet Oxygen Luminescence by Energy Transfer from Chlorine Molecules

An optical absorption (OA) band of interstitial dichlorine monoxide molecules with peak at 4.7 eV and halfwidth 0.94 eV is identified in F2 laser‐irradiated (ħω = 7.9 eV) synthetic silica glass bearing both interstitial O2 and Cl2 molecules. Alongside with intrinsic defects, this OA band can contribute to solarization of silica glasses produced from SiCl4. Although only the formation of ClClO is confirmed by its Raman signature, its structural isomer ClOCl may also contribute to this induced OA band. Thermal destruction of this band between 300 °C and 400 °C almost completely restores the preirradiation concentration of interstitial Cl2. An additional weak OA band at 3.5 eV is tentatively assigned to ClO2 molecules. The strongly forbidden 1272 nm infrared luminescence band of excited singlet O2 molecules is observed at 3–3.5 eV excitation, demonstrating an energy transfer process from photoexcited triplet Cl2 to O2. The energy transfer most likely occurs between Cl2 and O2 interstitial molecules located in neighboring nanosized interstitial voids in the structure of SiO2 glass network.

Synthesis, structure and photoluminescent properties of Eu:Gd2O3 nanophosphor synthesized by cw CO2 laser vaporization

Europium doped Gd2O3 sphere-like nanoparticles with dm = 9.3 ± 3.5 nm were synthesized by cw CO2 laser vaporization technique in a flowing mixture of argon and oxygen. According to XRD data, the Eu:Gd2O3 nanoparticles crystallize in the monoclinic symmetry class (C2/m space group). High-resolution luminescence spectroscopy study showed that the ultra-narrow 5D0 → 7F0 transition of Eu3+ demonstrates only two peaks corresponding to two inequivalent Cs positions of Eu3+ ion in monoclinic Gd2O3 lattice that is explained by the peculiarities of local environment of Eu3+ ion at these sites. The hypersensitive transition 5D0 → 7F2 dominates in the spectrum and is expanded to the red part of the spectrum in comparison with cubic Eu:Gd2O3 due to intense transitions terminating at higher-lying components of the crystal-field-split 7F2 state. In the luminescence spectrum, an additional weak band with the maximum at 407 nm corresponding to the electronic transitions 4f65 d1(7FJ) → 4f7(8S7/2) of Eu2+ was detected. The obtained values of chromaticity coordinates and absolute quantum yield are (0.644; 0.325) and ca. 1%, respectively. The phase transformations have been investigated using differential scanning calorimetry and thermogravimetry (50–1400 °C). After annealing in air at 700 °C, the monoclinic symmetry class of the Eu:Gd2O3 nanoparticles is preserved and the particle size increases to dm= 17.8 ± 6.1 nm. After annealing, the chromaticity coordinates (0.659; 0.334) and absolute quantum yield (ca. 4%) can be obtained using red phosphor based on monoclinic Gd2O3:Eu3+. The lifetime of the excited 5D0 state of Eu3+ in the annealed nanoparticles is longer than that in the as-synthesized nanoparticles, due to the suppression of nonradiative decay after annealing.

Electronic Spectrum of the Tropylium Cation in the Gas Phase

The structure and properties of the tropylium cation (C7H7+) have enthralled chemists since the prediction by Hückel in 1931 of the remarkable stability for cyclic, aromatic molecules containing six π-electrons. However, probing and understanding the excited electronic states of the isolated tropylium cation have proved challenging, as the accessible electronic transitions are weak, and there are difficulties in creating appreciable populations of the tropylium cation in the gas phase. Here, we present the first gas-phase S1 ←S0 electronic spectrum of the tropylium cation, recorded by resonance-enhanced photodissociation of weakly bound tropylium-Ar complexes. We demonstrate that the intensity of the symmetry-forbidden S1 ←S0 transition arises from Herzberg-Teller vibronic coupling between the S1 and S2 electronic states mediated by vibrational modes of e2' and e3' symmetry. The main geometry change upon excitation involves elongation of the C-C bonds. Multiconfigurational ab initio calculations predict that the S1 excited state is affected by the dynamical Jahn-Teller effect, which should lead to the appearance of additional weak bands that may be apparent in higher-resolution electronic spectra.

Formation of Short Zn-Zn Bonds Stabilized by Simple Cyanide and Isocyanide Ligands.

Cyanogen diluted in argon was reacted with laser ablated Zn atoms to produce the NCZnCN and NCZnZnCN cyanides and higher energy isocyanides ZnNC, CNZnNC, and CNZnZnNC, which were isolated in excess argon at 4 K. These reaction products, identified from the matrix infrared spectra of their -CN and -NC chromophore ligand stretching modes, were confirmed by 13 C and 15 N isotopic substitution and comparison with frequencies calculated by the B3LYP and CCSD(T) methods using the all electron aug-cc-pVTZ basis sets. The cyanide and isocyanide products were increased markedly by mercury arc UV photolysis, which covers the zinc atomic absorption. The above electronic structure calculations that produce appropriate ligand frequencies for these dizinc products also provide their Zn-Zn bond lengths: CCSD(T) calculations find a short 2.367 Å Zn-Zn bond in the NCZnZnCN cyanide, a shorter 2.347 Å Zn-Zn bond in the 37.4 kJ mol-1 higher energy isocyanide CNZnZnNC, and a longer 4.024 Å bond in the dizinc van der Waals dimer. Thus, the diatomic cyanide (-CN) and isocyanide (-NC) ligands are as capable of stabilizing the Zn-Zn bond as many much larger ligands based on their measured and our calculated Zn-Zn bond lengths. This is the first example of dizinc complexes stabilized by different ligand isomers. Additional weaker bands in this region can be assigned to the analogous trizinc molecules NCZnZnZnCN and CNZnZnZnNC.

Formation of Short Zn−Zn Bonds Stabilized by Simple Cyanide and Isocyanide Ligands

AbstractCyanogen diluted in argon was reacted with laser ablated Zn atoms to produce the NCZnCN and NCZnZnCN cyanides and higher energy isocyanides ZnNC, CNZnNC, and CNZnZnNC, which were isolated in excess argon at 4 K. These reaction products, identified from the matrix infrared spectra of their ‐CN and ‐NC chromophore ligand stretching modes, were confirmed by 13C and 15N isotopic substitution and comparison with frequencies calculated by the B3LYP and CCSD(T) methods using the all electron aug‐cc‐pVTZ basis sets. The cyanide and isocyanide products were increased markedly by mercury arc UV photolysis, which covers the zinc atomic absorption. The above electronic structure calculations that produce appropriate ligand frequencies for these dizinc products also provide their Zn−Zn bond lengths: CCSD(T) calculations find a short 2.367 Å Zn−Zn bond in the NCZnZnCN cyanide, a shorter 2.347 Å Zn−Zn bond in the 37.4 kJ mol−1 higher energy isocyanide CNZnZnNC, and a longer 4.024 Å bond in the dizinc van der Waals dimer. Thus, the diatomic cyanide (‐CN) and isocyanide (‐NC) ligands are as capable of stabilizing the Zn−Zn bond as many much larger ligands based on their measured and our calculated Zn−Zn bond lengths. This is the first example of dizinc complexes stabilized by different ligand isomers. Additional weaker bands in this region can be assigned to the analogous trizinc molecules NCZnZnZnCN and CNZnZnZnNC.

Infrared Spectroscopy of Size-Selected Hydrated Carbon Dioxide Radical Anions CO2 .- (H2 O)n (n=2-61) in the C-O Stretch Region.

Understanding the intrinsic properties of the hydrated carbon dioxide radical anions CO2 .−(H2O)n is relevant for electrochemical carbon dioxide functionalization. CO2 .−(H2O)n (n=2–61) is investigated by using infrared action spectroscopy in the 1150–2220 cm−1 region in an ICR (ion cyclotron resonance) cell cooled to T=80 K. The spectra show an absorption band around 1280 cm−1, which is assigned to the symmetric C−O stretching vibration ν s. It blueshifts with increasing cluster size, reaching the bulk value, within the experimental linewidth, for n=20. The antisymmetric C−O vibration ν as is strongly coupled with the water bending mode ν 2, causing a broad feature at approximately 1650 cm−1. For larger clusters, an additional broad and weak band appears above 1900 cm−1 similar to bulk water, which is assigned to a combination band of water bending and libration modes. Quantum chemical calculations provide insight into the interaction of CO2 .− with the hydrogen‐bonding network.

Excited-state properties of the central-cis isomer of the carotenoid peridinin

The central-cis isomer of the carotenoid peridinin, presumably 13-cis, was separated and studied with spectroscopic methods including static absorption, fluorescence and femtosecond time-resolved absorption. The investigations exposed differences in the photophysical properties of this isomer in respect to all-trans peridinin. Steady-state absorption spectroscopy revealed the presence of an additional weak absorption band at the long wavelength tail of the main S0 → S2 transition. Modelling of the hypothetical vibronic progression of the S0 → S1 electronic transition demonstrated that this weak band can be associated with a higher (0–2) vibronic band of the transition and that lower vibronic bands have negligible intensities due to a large displacement between the S0 and S1 states energy curves as also suggested by the spectral shape of steady-state fluorescence emission. Transient absorption studies demonstrated that the lifetime of the S1 state of the central-cis isomer is shorter compared to the all-trans counterpart by 6–16%, depending on the polarity of the solvent. On the other hand, molecular isomerization negligibly affects the lifetime of intramolecular charge transfer (ICT), which for both isomers is ∼10 ps in the polar solvent methanol.

Tungsten Hydride Phosphorus- and Arsenic-Bearing Molecules with Double and Triple W-P and W-As Bonds.

Laser ablation of tungsten metal provides W atoms which react with phosphine and arsine during condensation in excess argon and neon, leading to major new infrared (IR) absorptions. Annealing, UV irradiation, and deuterium substitution experiments coupled with electronic structure calculations at the density functional theory level led to the assignment of the observed IR absorptions to the E≡WH3 and HE═WH2 molecules for E = P and As. The potential energy surfaces for hydrogen transfer from PH3 to the W were calculated at the coupled-cluster CCSD(T)/complete basis set level. Additional weak bands in the phosphide and arsenide W-H stretching region are assigned to the molecules with loss of H from W, E≡WH2. The electronic structure calculations show that the E≡WH3 molecules have a W-E triple bond, the HE═WH2 molecules have a W-E double bond, and the H2E-WH molecules have a W-E single bond. The formation of multiple E-W bonds leads to increasing stability for the isomers.

Effect of Eu ion incorporation on the emission behavior of Y2O3 nanophosphors: A detailed study of structural and optical properties

In order to investigate the effect of doping concentration on the luminescence behavior of yttrium oxide (Y2O3) europium (Eu) doped nanoparticles were prepared by co-precipitation method. Incorporation of Eu ion in Y2O3 matrix is clearly reflected in structural and optical properties of the doped Y2O3 phosphor. Cathodoluminescence (CL) spectroscopy proves the presence of strong Eu3+ emissions along with the presence of an additional weak band corresponding to electronic transitions 4f65d1 (7FJ) – 4f7 (8S7/2) of the Eu2+. The presence of Eu3+ and Eu2+ ions in Y2O3 nanoparticles have been additionally confirmed by XPS analysis. Luminescence band corresponding to Eu3+ ions appears in both CL and photoluminescence (PL) spectra, covering the orange-red emissions from 580 to 710 nm. Vibrational properties analyzed through Raman spectroscopy have revealed the evolution of different peaks associated with Eu emission in the doped Y2O3 nanocrystals.

Effect of Erythropoietin, Iron Deficiency and Iron Overload on Liver Matriptase-2 (TMPRSS6) Protein Content in Mice and Rats.

Matriptase-2 (TMPRSS6) is an important negative regulator of hepcidin expression; however, the effects of iron overload or accelerated erythropoiesis on liver TMPRSS6 protein content in vivo are largely unknown. We determined TMPRSS6 protein content in plasma membrane-enriched fractions of liver homogenates by immunoblotting, using a commercial antibody raised against the catalytic domain of TMPRSS6. Plasma membrane-enriched fractions were obtained by centrifugation at 3000 g and washing. TMPRSS6 was detected in the 3000 g fraction as a 120 kDa full-length protein in both mice and rats. Feeding of iron-deficient diet as well as erythropoietin treatment increased TMPRSS6 protein content in rats and mice by a posttranscriptional mechanism; the increase in TMPRSS6 protein by erythropoietin was also observed in Bmp6-mutant mice. Administration of high doses of iron to mice (200, 350 and 700 mg/kg) decreased TMPRSS6 protein content. Hemojuvelin was detected in the plasma membrane-enriched fractions of control animals as a full length protein of approximately 52 kDa; in iron deficient animals, the full length protein was partially cleaved at the N-terminus, resulting in an additional weak band of approximately 47 kDa. In livers from hemojuvelin-mutant mice, TMPRSS6 protein content was strongly decreased, suggesting that intact hemojuvelin is necessary for stable TMPRSS6 expression in the membrane. Overall, the results demonstrate posttranscriptional regulation of liver TMPRSS6 protein by iron status and erythropoietin administration, and provide support for the interaction of TMPRSS6 and hemojuvelin proteins in vivo.

Single-crystal neutron diffraction and Raman spectroscopic study of hydroxylherderite, CaBePO4(OH,F)

AbstractThe crystal structure, H bonding and chemical composition of hydroxylherderite from the Bennett pegmatite, Buckfield, Oxford County, Maine, USA were investigated by single-crystal X-ray diffraction and neutron Laue diffraction, electron microprobe analysis in wavelength-dispersive mode, inductively coupled plasma-atomic emission spectrometry and polarized Raman spectroscopy [Ca(Na0.01Ca1.01)∑1.02Be(Be0.98Li0.01)∑0.99P(Si0.03P0.98)∑1.01O4(OH0.67F0.33)∑1,Z= 4,a= 9.7856(5),b= 7.6607(5),c= 4.8025(3) Å, β = 90.02(3)°,V= 360.02(4) Å3, space groupP21/a]. The neutron-structure refinement converged with fully anisotropic displacement parameters to give a final agreement indexR1= 0.0363 for 85 refined parameters and 1614 unique reflections withFo>4σ(Fo). The structure refinement was used to determine the H position and geometry of H bonding in the structure. OneHsite was found on theO5 anion with an O–H interatomic distance, corrected for “riding motion”, of 0.996(2) Å. The H bond of hydroxylherderite is bifurcated withO2 andO4 acceptors forming H bonds withO5⋯O2 = 3.163(1) Å,H⋯O2 = 2.544(2) ÅandO5–H⋯O2 = 121.8(1)°;O5⋯O4 = 3.081(1) Å,H⋯O4 = 2.428(2) Å andO5–H⋯O4 = 124.4(1)°. The highly non-linear O–H⋯O hydrogen bonds in hydroxylherderite and in the isotypic datolite [ideally CaBSiO4(OH)] are constrained by the tetrahedral network topology. Two main O–H stretching modes were observed in the Raman spectra at 3565 and 3620 cm–1, which are attributed to the bifurcated H bond. Two additional weak bands at 3575 and 3610 cm–1are attributed to Si–P disorder in the tetrahedral sites. Results of this study will contribute to the correlation of H-bonding geometry and O–H stretching frequencies of highly non-linear H bonds.

Halide impact on emission of mononuclear copper(i) complexes with pyrazolylpyrimidine and triphenylphosphine

A series of mononuclear heteroleptic copper(I) halide complexes, [CuL(PPh3)X] (X = Cl, Br, I), based on 4-(3,5-diphenyl-1H-pyrazol-1-yl)-6-(piperidin-1-yl)pyrimidine (L) and triphenylphosphine, have been synthesized by reaction between CuX (X = Cl, Br, I), L and PPh3 in a molar ratio of 1/1/1 in MeCN solutions. The copper atom, showing the distorted tetrahedral environment, is bound by the N,N-chelating ligand L, triphenylphosphine and a halide ion. The complexes [CuL(PPh3)Cl] and [CuL(PPh3)Br] are isostructural. In CH2Cl2 solutions, L and the complexes [CuL(PPh3)X] (X = Cl, Br, I) display a luminescence band with λ(max) = 377 nm and a lifetime of 1.9 ns (ligand-based luminescence (LL*)). However, the complex [CuL(PPh3)I] has an additional weak luminescence band with λ(max) = 681 nm and a lifetime of 96 ns of (3)MLCT origin. In the solid state, L shows the splitting of the luminescence band to λ(max) = 365 and 384 nm and a slight increase of the lifetime to 2.66 ns. Solid samples of the complexes [CuL(PPh3)X] demonstrate (3)MLCT luminescence bands at 620 nm (X = Cl), 605 nm (X = Br) and 559 nm (X = I) with lifetimes in the range 3.6-11.2 μs, whereas the LL* band (377 nm) is absent. Quantum yields and rate constants of radiative and nonradiative processes were determined in CH2Cl2 solutions and in the solid state for all complexes. The luminescence quantum yield and lifetimes for the solid samples increase in the order [CuL(PPh3)Cl] < [CuL(PPh3)Br] < [CuL(PPh3)I]. This is due to the increase of radiative decay and simultaneous suppression of nonradiative decay. The complex [CuL(PPh3)I] shows a high quantum yield of 29.4% and an excited state lifetime of 11.2 μs.

CARACTERIZAÇÃO DE CONCENTRADO E ISOLADO PROTÉICO EXTRAÍDO DE SEMENTES DE CUPUAÇU (Theobroma gradiflorum,Schum)

Summary This research describes the extraction of both a protein concentrate and isolate from the seeds of cupuassu (Theobroma grandiflorum Schum) using a mild extraction procedure, and provides the amino acid and electrophoretic profiles of the proteins of this Amazonian product. The pH of minimum solubility, considered as the isoelectric point representative of the proteins was 3.5. The mild extraction system was not capable of producing a protein concentrate and protein isolate containing more than 31.18 and 64.33% protein, respectively. From the electrophoretic profiles of the defatted flour, protein concentrate and protein isolate, three major bands were observed with approximate molecular weights between 20.03 and 39.79 kDa. Six additional weak bands were evident in the profiles of the defatted flour and the concentrate, but two of these were absent from the isolate. As inferred from the amino acid profiles of the flour, concentrate and isolate, the cupuassu seed proteins contain a composition nutritionally superior to that of cocoa for most of the amino acids.

Structure and linear spectroscopic properties of near IR polymethine dyes

We performed a detailed experimental investigation and quantum-chemical analysis of a new series of near IR polymethine dyes with 5-butyl-7,8-dihydrobenzo[ cd]furo[2,3- f]indolium terminal groups. We also synthesized and studied two neutral dyes, squaraine and tetraone, with the same terminal groups and performed a comparison of the spectroscopic properties of this set of “near IR” dyes (polymethine, squaraine, and tetraone) with an analogous set of “visible” dyes with simpler benzo[ e]indolium terminal groups. From these measurements, we find that the dyes with dihydrobenzo[ cd]furo[2,3- f]indolium terminal groups are characterized by a remarkably large shift ≈300 nm (≈200 nm for tetraone) of their absorption bands towards the red region. We discuss the difference in electronic structure for these molecules and show that the “near IR” dyes are characterized by an additional weak fluorescence band from the higher lying excited states connected with the terminal groups. Absorption spectra for the longest polymethines are solvent-dependent and are characterized by a broadening of the main band in polar solvents, which is explained by ground state symmetry breaking and reduced charge delocalization within the polymethine chromophore. The results of these experiments combined with the agreement of quantum chemical calculations moves us closer to a predictive capability for structure–property relations in cyanine-like molecules.

Surface-Enhanced Infrared Absorption Spectroscopic Studies of Adsorbed Nitrate, Nitric Oxide, and Related Compounds 1: Reduction of Adsorbed NO on a Platinum Electrode

Surface-enhanced infrared absorption spectroscopy (SEIRA) was used to examine the adsorption state of nitrogen monoxide (nitric oxide, NO) and the reduction of the adsorbed species. The SEIRA spectra gave two distinct bands at 1723-1733 and 1575-1607 cm-1 with an additional weak band at 1656-1676 cm-1 at 0.20 V, the frequencies of which are slightly dependent on the surface coverage. The former two bands are attributed to the on-top and bridged NO, respectively. While the on-top NO stably remained on the surface in the potential range of 0.05 -0.60 V, the bridged NO decreased in its intensity with increasing electrode potential. The reduction of the adsorbed NO obeys first-order kinetics with respect to the adsorbed NO. The rate constants are 2.24 +/- 0.03 and 0.24 +/- 0.09 s-1 at -0.10 V for the on-top and bridged NO, respectively. Tafel slopes obtained from the potential dependence of the rate constant indicate that the rate-determining step is the first electron-transfer process.

Excited states of C2H4 studied by (3 + 1) and (3 + 2) REMPI spectroscopy: disentangling the lowest Rydberg series from the strong π–π* V ← N transition

(3 + 1) and (3 + 2) Resonantly EnhancedMultiphoton (REMPI) spectroscopy has been carried out to study the Rydberg states of C2H4 in the region 55000–83000 cm−1. Differences and similarities were observed between these three-photon spectra and the one-photon absorption spectrum. First, the disappearance of the strong π−π* V ← N valence transition from the REMPI spectra allowed disentanglement of the vibrational structure of the 3s Rydberg transition from the V ← N quasi-continuum, and a search for additional weak transitions. Earlier vibrational assignments from the absorption spectrum have been confirmed in the REMPI analysis of the 3s ← N and ns, nd ← N transition systems, although with very different band intensities. This analysis has provided additional weak band assignments involving the ν3 mode in the observed Rydberg transitions. New electronic components (3dπ y , 4dπ y , 5dπ y ) of the nd complex, which are three-photon allowed but one-photon forbidden, have been tentatively assigned. The photoelectron (PES) spectra of the 3s and 3dσ lowest vibrational levels have revealed a deviation from a pure Rydberg character, in apparent contradiction with previous (2 + 1) REMPI-PES data involving gerade vibronic levels of the 3s Rydberg state, which led to a prominent Rydberg character for this state. Rydberg–valence and Rydberg–Rydberg vibronic interactions mediated via non-symmetric modes could explain the different behaviour between gerade and ungerade vibronic levels of the ethylene Rydberg states. †Permanent address: Atomic Energy Commission of Syria, PO BOX 6091, Damascus, Syria.

Bathochromic shift of the Q-bands of octakis(p-t-butylbenzyloxy)phthalocyanines with magnesium(II), nickel(II) and copper(II) in a solvent mixture of chloroform and acetic acid

1,4,8,11,15,18,22,25-octakis(p-t-butylbenzyloxy)phthalocyanine complexes of magnesium(II), nickel(II) and copper(II) were prepared by refluxing the propanol solution of 3,6-di(p-t-butylbenzyloxy)phthalonitrile in the presence of magnesium turnings. The complexes showed intense Q-bands between 740 and 750 nm in chloroform. The magnesium(II) complex showed an additional weak band at 807 nm in chloroform, while the nickel(II) and copper(II) did not. The Q-band of the magnesium(II) species was red-shifted with increase of acetic acid in the solvent mixture of chloroform and acetic acid; 745, (765, 807) and (810, 868 nm) in chloroform, 0.1% (v/v) acetic acid and 60% (v/v) acetic acid, respectively. The magnesium(II) complex has bands at 900 and 999 nm in trifluoroacetic acid. In the solvent mixture of 1% (v/v) acetic acid, the red-shift of the Q-band was larger for the magnesium(II) derivative, a little for the nickel(II) and scarcely for the copper(II), respectively. The shift was explained by protonation of the external nitrogen atoms of the phthalocyanine ring.

Characterisation of dispersed organic matter from lower Palaeozoic metasedimentary rocks by organic petrography, X-ray diffraction and micro-Raman spectroscopy analyses

Dispersed organic matter (DOM) concentrates of C-rich rocks from areas with different metamorphic characteristics were studied by organic petrography, X-ray diffraction (XRD) and micro-Raman spectroscopy analysis. The concentrates contain several types of DOM with different morphologies, reflectance, X-ray diffraction and micro-Raman characteristics. Four different morphological types were identified in the two studied areas. The different types have different distributions and their reflectance is quite variable in the four types, with a dominance of the highest reflectance values in the DOM from the area with the highest metamorphic grade. XRD analyses of samples from the areas reveal the presence of fine graphite together with non-graphitised carbons. The Raman spectral profiles show the usual bands G (1582 cm −1) and D1 (1350 cm −1), on the first-order Raman spectrum, and S1 (2700 cm −1) on the second-order spectrum. Additional weaker bands, D2 (1620 cm −1), and more rarely D3 (1500 cm −1) and S2 (2900 cm −1), are present. These are characteristic for disordered carbons in the different types of DOM and in both studied areas. However, the Raman parameters (D1/G intensity area ratio and the frequency and width of G band) indicate variable degrees of organisation in all DOM types. The existence of different types of DOM with different degrees of ordering in the same lithologies and metamorphic grade seems to be related to different organic precursors, as they are graphitised to different extents under the same metamorphic conditions. However, in the same lithologies and metamorphic grade, the existence of various stages of graphitisation within the same type of DOM can only be explained though the interaction of DOM with the metamorphic fluids present in the rocks. The ordering graphitisation process may be due to the existence of metamorphic fluid circulation events with a variety of compositions.