Showing papers on "Absorption spectroscopy published in 1980"

Thermo‐optical spectroscopy: Detection by the ’’mirage effect’’

Abstract: A new thermo‐optical method based on the sensitive detection of thermal gradients adjacent to heated sample surfaces is described. Room‐ and low‐temperature experiments were performed using this technique, and its advantages over different methods are discussed.

Detection of NO3 in the polluted troposphere by differential optical absorption

Abstract: The nitrate radical, NO3, has been identified and measured for the first time in the polluted troposphere using long path (970 and 750 m) differential optical absorption spectroscopy at two sites in the Los Angeles basin. NO3 concentrations of up to 355 ppt were measured using the strong NO3 absorption bands at 623 and 662 nm. During pollution episodes from September 11 to September 19, 1979 concentrations increased sharply after sunset and peaked about one hour later at ∼ 20:00 (PDT). In many other cases peak concentrations were much lower and sometimes below the detection limit of several ppt. Possible sinks for the NO3 radical under polluted conditions are considered, including reaction with NO, reaction with organic species, and the hydrolysis of N2O5 for which a new upper limit rate constant is derived.

Porphyrins. 40. Electronic spectra and four-orbital energies of free-base, zinc, copper, and palladium tetrakis(perfluorophenyl)porphyrins

Abstract: Absorption and emission spectra and emission quantum yields are given for free-base (H/sub 2/), Zn, Cu, and Pd derivatives of tetrakis(perfluorophenyl)porphyrin (TFPP). The four-orbital model is used to rationalize differences in the optical properties among the derivatives of TFPP and the same derivatives of porphine (P), octaethylporphyrin (OEP), and tetraphenylporphyrin (TPP). It is concluded from absorption data that the energy difference between the two excited singlets, i.e., /sup 1/E(a/sub 2u/,e/sug g/) - /sup 1/E(a/sub 1u/,e/sub g/), decreases along the series Pd > Cu > Zn > H/sub 2/ and also along the series OEP > P > TFPP > TPP. The theory and date are reviewed, and it is concluded that the energy difference between the two excited triplets, i.e., /sup 3/E(a/sub 2u/,e/sub g/) - /sup 3/E(a/sub 1u/,e/sub g/), also decreases along these series. However the condition of degeneracy, e.g., /sup 1/E(a/sub 2u/,e/sub g/) - /sup 1/E(a/sub 1u/,e/sub g/) = 0, occurs for different molecules in the singlet and triplet cases. Theory also suggests that if /sup 3/E(a/sub 2u/,e/sub g/) > /sup 3/E(a/sub 1u/,e/sub g), the molecule should form a /sup 2/A/sub 1u/ cation radical and if /sup 3/E(a/sub 2u/,e/sub g/) < /sup 3/E(a/sub 1u/,e/sub g/) the molecule should formmore » a /sup 2/A/sub 2u/ radical. 4 figures, 2 tables.« less

Interaction of metal particles with adsorbed dye molecules: absorption and luminescence.

Abstract: Absorption, luminescence, and excitation luminescence studies of dye molecules adsorbed onto ultrathin, variable-thickness silver films show strong coupling of the particle plasma resonances to the molecules. Luminescence from the dye is increased by excitation transfer from the silver particles for certain film thickness. Increased luminescence has also been observed from dyes on Au and Cu films.

Use of one‐electron theory for the interpretation of near edge structure in K‐shell x‐ray absorption spectra of transition metal complexes

Abstract: We report the results of multiple scattered wave SCF X‐alpha calculations of the one‐electron cross section for K‐shell photoabsorption in the molecular complexes MoO4−−, CrO4−−, and MoS4−−. We show that the method can successfully account for energy separations and relative cross sections of spectral features both below and above the K‐shell ionization threshold. Furthermore, we show: (a) that the first fairly intense peak on the low energy side of the rising edge for molybdate and chromate is due to a dipole allowed transition to a bound antibonding state of mainly nd character on the metal ion; this transition is possible because of the mixing with the ligand p orbitals having the proper T2 symmetry induced by the tetrahedral molecular potential; (b) the shoulder on the rising absorption edge can be explained by the beginning of the steplike continuum absorption when convolved with a Lorentzian function of frequency to imitate lifetime and monochromator broadening: (c) the main absorption peak is due t...

Measurement of gain and absorption spectra in AlGaAs buried heterostructure lasers

Abstract: A new method for measuring absorption and gain spectra of lasers is presented. These spectra are deduced from measurements of spontaneous emission spectra at different laser currents supplemented by measurements of the laser line energy and the differential quantum efficiency. The spontaneous emission emerged from the side of the laser after traveling through a transparent cladding layer. At each current, the bias energy eV is determined. A simple theoretical model is used to convert eV to minority carrier density. The method is based on the application of general relations between the rates of spontaneous emission, stimulated emission, and optical absorption. A new general proof of these relations is presented. The gain versus carrier density relation at the laser line energy is measured for four samples having different active layer doping or Al composition. Gain increased superlinearly with carrier density in undoped and n‐type samples and increased slightly sublinearly in a p‐type sample. The losses a...

The ultraviolet absorption spectrum of liquid water

Abstract: The absorptivities of carefully purified water have been measured at 1 nm intervals in the wavelength range 196 to 320 nm. The measured absorptivities fell monotonically from a value of (1.26±0.03) m−1 at 196 nm, to a value of (0.0100±0.0006) m−1 at 320 nm. The water was purified by ion–exchange, followed by four subsequent distillations, the first being carried out under mild oxidizing conditions, and the last being performed in all‐silica apparatus, the water vapor being heated to a temperature of 870 K in the presence of oxygen to remove residual organic impurities. The absorptivities were measured using a differential pathlength method and a correction for the effect of double reflections in the absorption cells was derived and applied to the data. The measured absorptivities were much lower than all previously reported values in the 200–300 nm region, but gave considerably better agreement with theory and aligned well with the edge of a set of recent vacuum UV measurements on high purity water. It ap...

Vibrational relaxation in jet‐cooled alkyl benzenes. I.Absorption spectra

Abstract: Fluorescence excitation spectra of a series of alkylbenzenes cooled in a supersonic free jet have been obtained for the first 1000 cm−1 region of the 1B2(ππ*)←1A1 ultraviolet absorption spectrum. The series includes all n‐alkylbenzenes up to n‐hexyl together with isopropyl‐ and tert‐butylbenzene. As with toluene, the spectra in this region for all alkylbenzenes is found to be dominated by vibrations of five ring modes: 6a, 6b, 1, 12, and 18a. Three of these—the ’’system modes’’ (6b, 12, 18a)—are found to be largely invariant to changes in the alkyl chain length and type— the ’’bath.’’ For n‐alkylbenzenes with chain length of three or higher, spectra of two distinct conformations are observed with roughly equal intensity. These conformations are distinguished by configuration about the 1–2 carbon–carbon bond of the alkyl chain. When this configuration is trans [n‐(t)‐alkylbenzene], the alkyl chain extends away from the phenyl ring leaving the ring free to van der Waals complex binding on both sides of the ...

Jet‐cooled naphthalene. I. Absorption spectra and line profiles

Abstract: Fluorescence excitation spectra have been recorded for the first 6000 cm−1 of the ultraviolet spectrum of h8‐ and d8‐naphthalene cooled in a supersonic free jet. Measured profiles of vibronic bands in these spectra display a monotonically increasing width as a function of vibrational energy (Ev) in the excited electronic state. The high fluorescence quantum yield and relatively constant fluorescence lifetimes in these spectral regions require the measured line broadening to be assigned to intramolecular vibrational relaxation (IVR) within the excited electronic state. The rate of this IVR process as measured by the width of the broadened profiles increases smoothly from 9×1010 sec−1 at Ev=3068 cm−1 to 7×1011 sec−1 at Ev=5200 cm−1 for h8‐naphthalene. Line profiles of d8‐naphthalene in this same spectral region are found to be ∼50% wider.

Infrared absorption spectra of SiO2 precipitates of various shapes in silicon: calculated and experimental

Abstract: It is shown that the infrared absorption band at 1230 cm−1, observed under certain conditions of oxygen precipitation in silicon, is the LO mode of SiO2 The LO mode, which is normally infrared inactive, becomes infrared active under the condition of polarization of small (<036 μm) platelets in an appropriate dielectric matrix (silicon) Infrared absorption spectra of SiO2 particles of various shapes, imbedded in silicon, have been calculated For platelet SiO2 precipitates, the spectrum shows an absorption band at 1215 cm−1, which is reasonably close to the observed band at 1230 cm−1 For SiO2 precipitates of other shapes the spectra do not exhibit this absorption band Instead, they exhibit a slightly weaker primary absorption band at 1095 cm−1, the TO mode, and a very weak band at 1170 cm−1, which is a mixed mode of longitudinal and transverse optical phonons

Sensitivity enhancement of laser absorption spectroscopy by magnetic rotation effect

Abstract: The use of magnetic rotation spectroscopy (Faraday effect) to reduce the effects of source noise and improve sensitivity of spectroscopy with color center lasers has been analyzed theoretically and tested experimentally on the vibrational overtone band of NO. Sensitivity improvement of a factor of 30 compared with simple Zeeman modulation has been demonstrated. As an example of this technique, the first observation of the fundamental vibrational band of the OH radical in absorption is reported.

Nickel, a component of factor F430 from Methanobacterium thermoautotrophicum

Abstract: Methanobacterium thermoautotrophicum, growing on medium supplemented with 2 μmol 63NiCl2/l, was found to take up 1.2 μmol 63Ni per g cells (dry weight). More than 70% of the radioisotope was incorporated into a compound, which dissociated from the protein fraction after heat treatment, was soluble in 70% acetone, and could be purified by chromatography on QAE-Sephadex A-25, Sephadex G-25, and DEAE cellulose. The purified 63Ni labelled compound had an absorption spectrum and properties identical to those of factor F430 and is therefore considered to be identical with factor F430.

Spectroscopy of Cr 3+ in Glasses: Fano Antiresonances and Vibronic "Lamb Shift"

Abstract: Absorption spectra of ${\mathrm{Cr}}^{3+}$-doped glasses exhibit features which are interpreted as Fano antiresonances resulting from interaction of $^{2}E$ and $^{2}T_{1}$ states with a vibrationally broadened $^{4}T_{2}$. Inhomogeneous line broadening in glass permits the observation of a shift of sharp levels due to interaction with the quasicontinuum.

The MPI spectrum of expansion-cooled ammonia: Photophysics and new assignments of electronic excited states

Abstract: The two‐ and three‐photon spectrum of expansion‐cooled ammonia has been recorded in the 380–500 nm region using multiphoton ionization (MPI) detection. In addition, the vacuum ultraviolet spectrum of gas phase ammonia has been measured photoelectrically in the 125–160 nm region. Features due to transitions to eleven electronic states are assigned in the 5.7–9.3 eV energy range, where only five band systems were previously assigned. By utilizing the spectral simplification provided by expansion cooling, the different selection rules for multiphoton absorption, and the differences between the MPI and VUV spectra, assignments can be made with much more certainty. Three previously assigned band systems have been reassigned, and seven additional electronic states identified. It is found that states arising from nd orbitals are responsible for the most intense features in the VUV spectrum, in contrast to previous experimental and theoretical work where they were excluded from consideration. Evidence is found fo...

X-ray absorption spectroscopy of xanthine oxidase. The molybdenum centres of the functional and the desulpho forms.

Abstract: X-ray absorption spectra have been recorded for the molybdenum K-edge region of xanthine oxidase. Both the absorption edge and the extended fine structure (e.x.a.f.s.) regions were investigated. Spectra were obtained for samples of the desulpho enzyme as well as for mixtures of this with the active enzyme. The spectrum of the pure active form was then obtained by difference. The desulpho enzyme shows a pronounced step in the absorption edge, of a type previously associated terminal oxygen ligands. In the active enzyme this step has decreased markedly. Satisfactory simulations of the e.x.a.f.s. spectrum of the desulpho enzyme could be obtained by assuming the molybdenum to be bonded to two terminal oxygen atoms (Mo = O about .175 nm), two sulphur atoms (presumably from cysteine residues, Mo-S about .0250 nm) and one sulphur atom (presumably from a methionine residue, Mo-S about 0.290 nm). E.x.a.f.s. of the active enzyme differed appreciably from this. In keeping with earlier proposals [Gutteridge, Tanner & Bray (1978) Biochem. J. 175, 887-897], the spectrum of the active enzyme could be simulated if a sulphur atom at about 0.225 nm (i.e. presumably a terminal sulphur atom) replaced one of the terminal oxygen atoms of the desulpho from, with small changes in the other bond distances. Validity of the interpretative procedures, which involved phase shift and amplitude calculations ab initio, was demonstrated by using low molecular weight compounds of known structure.

Coordination of Ti in TiO2SiO2 glass by X-ray absorption spectroscopy

Abstract: Evidence from both the extended X-ray absorption fine structure (EXAFS) and near-edge regions of the Ti K-edge X-ray absorption spectrum for TiO2SiO2 glasses has been examined to determine the coordination geometry of the Ti4+ ion. It is concluded that this geometry is primarily a four-fold coordination, with a small fraction of the Ti4+ ions having six-fold coordination and a longer TiO bond length. The ratio of six-fold to four-fold coordination is seen to increase with increased TiO2 content in the glass.

Photoelectrochemical properties of metalloporphyrins

Abstract: The photovoltaic responses of meso tetraphenyl-, meso tetra-propyl- and octaethyl-porphyrins, porphines, chlorins, cofacial diporphyrins and mesoporphyrin IX diesters were investigated using two cell configurations: Al| Porphyrin |Ag, and Al| Porphyrin | Fe(CN)6−3, Fe(CN)6−4 |Pt. We found (1) that the Al–porphyrin interface is photoactive: the action spectra closely follow the absorption spectra of the porphyrins, and this interface is best described as a semiconductor–insulator–metal diode consisting of porphyrin |A12O3 |Al; (2) that within a homologous series, in which the porphyrin skeleton is fixed but the metal is varied, the quantum yields parallel the ease of oxidation of the porphyrin in nonaqueous solvents. The more easily oxidised compounds exhibit the higher quantum yields; (3) no obvious correlations are found with the luminescent properties of the porphyrins in solution; (4) the morphology of the films influences the quantum yields: amorphous films are better than microcrystalline ones; and (5) the most efficient cells reach quantum yields of ∼0.2 and energy efficiencies of ∼1% for monochromatic light at the peak of the action spectrum in the region of 400–450 nm.

CO and Temperature Measurements in a Flat Flame by Laser Ab orption Spectroscopy and Probe Techniques

Abstract: Carbon monoxide and temperature have been measured in the post-flame region of laminar, pre-mixed methane/air flat flames at atmospheric pressure using both laser absorption spectroscopy and conventional probe techniques. The laser absorption measurements employed a tunable diode laser to record fully resolved absorption lines in the fundamental band of CO near 4.7 microns. Probe measurements were made with thermocouples and sampling microprobes (uncooled quartz and water-cooled stainless steel). The extracted gases were analyzed for CO and CO2 using NDIR instruments. The laser absorption measurements of CO in rich flames were in good agreement with chemical equilibrium calculations based on metered fuel and air flow-rates and measured local temperature. In lean flames, measured levels of CO exceeded equilibrium values, as expected, due to incomplete reaction of CO to CO2 near the flame front. Temperatures inferred from the relative absorption in lines from different vibrational levels were in go...

Spectral adsorption properties of natural watres: contribtion of the soluble and particulate fractions to light absorption in some inland watres of south-eastern Australia

Abstract: A method has been developed for measuring the absorption spectra, and calculating the in situ absorption coefficients, of the particulate fraction (tripton/phytoplankton) of natural waters. The procedure involves concentrating the particulate fraction by filtration followed by resuspension in a smaller volume, and measuring the absorption spectrum with the help of an integrating sphere to minimize the effects of light scattering. The method has been applied to seven inland water bodies in the southern tablelands of New South Wales and the Australian Capital Territory. For comparative purposes the absorption spectra. and in situ absorption coefficients, of the soluble colouring matter (gilvin, gelbstoff) have also been measured. The absorption coefficients have been used to calculate what part of the total absorbed photosynthetically active radiation (PAR) is captured by each of the three major absorbing components. In clear but rather coloured waters, gilvin absorbs most of the quanta, followed by water itself. In two waters with fairly high phytoplankton levels, the particulate fraction absorbs as much PAR as the water, but gilvin still absorbs rather more than either. In highly turbid waters, the particulate fraction (consisting mainly of tripton) absorbs most of the quanta. The data show that tripton has an absorption spectrum in the visible region. which rises steadily with decreasing wavelength: this is attributed to humic materials. It is clear that in turbid waters the inanimate particulate fraction (tripton) is a major light absorber, in addition to being the most important light scatterer.

Vibronic Contributions to Ligand-Induced Pseudo-Quadrupole Absorption of Rare-Earth Ions

Abstract: The intensities of certain lines in the absorption spectra of rare-earth or actinide ions are very sensitive to the neighboring ligands. The contributions to these intensities coming from vibronic transitions (combined electronic and vibrational transitions) are calculated by tensorial techniques with particular reference to octahedral complexes. The expansions that are used possess leading terms that indicate that the strongest vibronic lines should be associated with electronic transitions that satisfy the selection rules on J (the total angular momentum) that are identical to those for quadrupole radiation. General agreement is obtained with the recent work of Faulkner and Richardson on the transition 7F0 → 5D2 of Eu3+, though some of the approximations and assumptions, as well as much of the mathematics, are different.

Studies on monolayers. 1. Surface tension and absorption spectroscopic measurements of monolayers of surface-active azo and stilbene dyes

Abstract: In order to develop new molecules as function components of monolayer assemblies, a series of 9 surface-active azo and stilbene compounds are synthesized. Their monolayer properties at the air-water interface are studied by surface pressure-surface area measurements and spectroscopic techniques. The results show that small changes in the molecular structure of the surfactants (such as, length of the fatty acid chain and type of the chromphore) have an immense influence on the monolayer properties. For monolayers of compounds I and III-VIII, van der Walls-like isotherms are obtained, which show a liquid expanded state, a phase transition region, and a condensed state. From monolayer absorbance spectra it is found that in the liquid expanded state at 100 to 110 sq angstroms/molecule the chromphores lie flatly on the water surface, forming monomers. The phase transition region of the isotherms can be assigned to a change of orientation of the chromophore axis (horizontal to vertical) and an aggregation process of the chromophores (monomers to H aggregates). 20 references.