Showing papers on "Absorption band published in 1986"
TL;DR: Reaction centers from the photosynthetic bacterium Rhodopseudomonas viridis have been excited within the near-infrared absorption bands of the dimeric primary donor, of the "accessory" bacteriochlorophylls (B), and of the bacteriopheophytins (H) by using laser pulses of 150-fsec duration, and it is found no indication that an accessory bacterio chlorophyll is involved as a resolvable intermediary acceptor in
Abstract: Reaction centers from the photosynthetic bacterium Rhodopseudomonas viridis have been excited within the near-infrared absorption bands of the dimeric primary donor (P), of the “accessory” bacteriochlorophylls (B), and of the bacteriopheophytins (H) by using laser pulses of 150-fsec duration. The transfer of excitation energy between H, B, and P occurs in slightly less than 100 fsec and leads to the ultrafast formation of an excited state of P. This state is characterized by a broad absorption spectrum and exhibits stimulated emission. It decays in 2.8 ± 0.2 psec with the simultaneous oxidation of the primary donor and reduction of the bacteriopheophytin acceptor, which have been monitored at 545, 675, 815, 830, and 1310 nm. Although a transient bleaching relaxing in 400 ± 100 fsec is specifically observed upon excitation and observation in the 830-nm absorption band, we have found no indication that an accessory bacteriochlorophyll is involved as a resolvable intermediary acceptor in the primary electron transfer process.
228 citations
TL;DR: In this article, an analogue of chlorophyll a, when adsorbed on colloidal TiO/sub 2/ can participate in the sensitization process by injecting electrons from its excited states into the conduction band of the semiconductor.
Abstract: Chlorophyllin, an analogue of chlorophyll a, when adsorbed on colloidal TiO/sub 2/ can participate in the sensitization process by injecting electrons from its excited states into the conduction band of the semiconductor. Upon excitation in its absorption band, 90% of the fluorescence emission of chlorophyllin could be quenched by colloidal TiO/sub 2/. The apparent association constant for the association between colloidal TiO/sub 2/ and chlorophyllin, as measured from the fluorescence quenching data, was 2 x 10/sup 4/ M/sup -1/. Picosecond lifetime measurements gave the rate constant for the electron injection process from the excited singlet state into the conduction band of the semiconductor as 4.2 x 10/sup 9/ s/sup -1/. The net charge transfer across the sensitizer-semiconductor interface was investigated with the laser flash photolysis and time-resolved microwave absorption techniques. Analysis of the transient absorption spectrum confirmed the generation of the cation radical of chlorphyllin with a quantum yield of 0.015. 32 references, 8 figures, 1 table.
173 citations
TL;DR: The photofragmentation dynamics of H2O molecules following vacuum ultraviolet laser excitation at wavelengths within the B1A1-X 1A1 absorption band have been investigated using a novel from-of-photofragment translational spectroscopy analysis of the nascent H atom time-offlight spectra.
Abstract: The photofragmentation dynamics of H2O molecules following vacuum ultraviolet laser excitation at wavelengths within the B1A1–X1A1 absorption band have been investigated using a novel from of photofragment translational spectroscopy Analysis of the nascent H atom time-of-flight spectra confirms the importance of the dissociation channel leading to ground-state H + OH products In addition, it reveals that the OH(X) fragments are formed predominantly in their zero-point vibrational level with a highly excited, inverted rotational-state population distribution A consideration of the topology of the various potential-energy surfaces sampled by the H2O molecules during this electronically non-adiabatic dissociation process suggests a likely explanation for this observed pattern of energy disposal
105 citations
Journal Article•
TL;DR: In this article, the photofragmentation dynamics of H2O molecules following vacuum ultraviolet laser excitation at wavelengths within the B1A1-X 1A1 absorption band have been investigated using a novel from-of-photofragment translational spectroscopy.
Abstract: The photofragmentation dynamics of H2O molecules following vacuum ultraviolet laser excitation at wavelengths within the B1A1–X1A1 absorption band have been investigated using a novel from of photofragment translational spectroscopy. Analysis of the nascent H atom time-of-flight spectra confirms the importance of the dissociation channel leading to ground-state H + OH products. In addition, it reveals that the OH(X) fragments are formed predominantly in their zero-point vibrational level with a highly excited, inverted rotational-state population distribution. A consideration of the topology of the various potential-energy surfaces sampled by the H2O molecules during this electronically non-adiabatic dissociation process suggests a likely explanation for this observed pattern of energy disposal.
97 citations
TL;DR: The change in absorbance (hole spectrum) of the primary electron donor (P870) in bacterial photosynthetic reaction centers has been studied at 1.5-2.1 K following narrow-band excitation at several wavelengths within the P870 absorption band as discussed by the authors.
81 citations
TL;DR: In this paper, a series of Mg doped congruent LiNbO3 crystals were investigated by UV a nd IR spectrophotometry and AC conductivity.
75 citations
TL;DR: The change in absorption of the primary electron donor in R. viridis reaction centers (P960) has been measured at 1.4-2.1 K following narrow bandwidth excitation at many wavelengths within the P960 absorption band as mentioned in this paper.
70 citations
TL;DR: In this paper, the absorption, excitation and emission spectra of Athabasca (Alberta, Canada) asphaltene and five of its fractions separated according to molecular weight (MW) by gel permeation chromatography (g.p.c.) on Bio-Beads SX-1.
70 citations
TL;DR: The defect center responsible for the 2 eV absorption band induced in pure silica core fibers by 60Co γ-rays is discussed in this paper, where the defect center is considered to be NBOHC.
Abstract: The defect center causing the 2 eV absorption band induced in pure silica core fibers by 60Co γ-rays is discussed. The 2 eV band and non-bridging oxygen hole center (NBOHC, SI–O) show almost the same thermal annealing characteristics. The peak wavelength of the 2 eV band in low-OH (6 ppm) fibers is 630 nm, but shifts to shorter wavelengths according to the amount of OH group the sample contains, and appears at 600 nm in high-OH (700 ppm) fibers. The peak shape is broader in high-OH fibers than in low-OH fibers. This shift and broadening is attributable to a hydrogen bond between NBOHC and a hydrogen atom. Based on the above results, the defect center responsible for the 2 eV band is considered to be NBOHC.
67 citations
01 Sep 1986
TL;DR: In this article, the authors proposed that H2O molecules occur as structural constituents entering the M site of the sanidine structure, where the plane of the H 2O molecules lies parallel to the symmetry plane.
Abstract: Polarizedinfrared (IR) spectra of sanidine crystals from Volkesfeld, Eifel show the existence of two broad pleochroic absorption bands at 3,400 and 3,050 cm−1. Because overtones near 5,150 cm−1 were observed, the former bands are assigned to OH stretching frequencies of H2O molecules. On the basis of the pleochroic scheme of the bands it is proposed that H2O molecules occur as structural constituents entering theM site of the sanidine structure; the plane of the H2O molecules lies parallel to the symmetry plane.
65 citations
TL;DR: The current status of reflection-absorption infrared spectroscopy (RAIRS) is reviewed with examples illustrating its application to studies of structural chemical transformations at surfaces in this article, and the prospects for the future are briefly discussed including the use of synchrotron and laser i.r. sources.
TL;DR: In this article, reaction centers from the photosynthetic bacterium Rhodopseudomonas sphaeroides have been excited either in the bacteriopheophytin band at 760 nm or in the accessory bacteriochlorophyll (B) band around 800 nm with laser pulses of 150 fs duration.
TL;DR: In this paper, the relative values of polarization angles of seven in-plane and twelve out-of-plane polarized IR transitions of 2 relative to the π pi * transition moment were determined.
Abstract: Irradiation of matrix-isolated dimethyldiazidosilane yields dimethylsilylene (1) as the major product. Photoselection on the 450-nm absorption band of 1 with polarized 488-nm light, which converts 1 into 1-methylsilene (2), permitted the assignment of six IR transitions of 1 and twelve IR transitions of 2 as in-plane or out-of-plane polarized. Photoselection on the 260-nm absorption band of 2 with polarized 248-nm light, which converts 2 back into 1, allowed a determination of the absolute values of polarization angles of seven in-plane polarized IR transitions of 2 relative to the ..pi pi..* transition moment. The resulting map of the IR transition moment directions in the molecule of 1 provides strong support for the detailed assignment of the nature of the vibrational motions involved. Along with other data, the results leave very little doubt as to the correctness of the structural and vibrational assignments in 1 and 2. 8 references, 6 figures, 2 tables.
TL;DR: In this article, the authors demonstrate thermal dissociation of up to 75% of oxygen-vacancy centers by monitoring their destruction in irradiated and annealed crystals and calibrating the strength of the infrared 830 cm−1 absorption band via a novel procedure.
Abstract: We have proposed previously that the extremely high rate of single diffusion jumps of oxygen atoms in silicon during electron irradiation of crystals above 300 °C is due to the sequential trapping and detrapping of vacancies. In support of this proposal we now demonstrate thermal dissociation of up to 75% of oxygen‐vacancy centers by monitoring their destruction in irradiated and annealed crystals. An important new step is the calibration of the strength of the infrared 830 cm−1 absorption band via a novel procedure to give the concentration of oxygen‐vacancy complexes in crystals.
TL;DR: In this article, the effect of 1.7 MeV electrons on the coloration of Yb 3+ doped BaF 2 /ThF 4 base fluoride glasses has been investigated.
Abstract: The effect of 1.7 MeV electrons on the coloration of Yb 3+ doped BaF 2 /ThF 4 base fluoride glasses has been investigated. Irradiation at 80 K produces a prominent absorption band at 302 nm. At room temperature, the radiation induced absorption is quite small in these glasses when compared with the absorption in fluorizirconate glasses. The photochemical damage mechanism is dominant. The optical absorption and emission spectra as well as the fluorescence lifetime of Yb 3+ ion transitions have been measured. The measured lifetimes are compared with the calculated radiative lifetimes.
TL;DR: In this paper, the effect of nonequivalent Cr sites on room temperature tunable-laser action has been investigated from the absorption and the excitation spectra, and a broad absorption band peaked near 750 nm does not contribute to the Cr emission.
Abstract: Room-temperature tunable-laser action has been observed in Cr-doped SrAlF5. The measured tuning range is 852–947 nm in a quasi-cw laser mode. The effect of nonequivalent Cr sites in SrAlF5 is studied from the absorption and the excitation spectra. A broad absorption band peaked near 750 nm does not contribute to the Cr emission and appears to be associated with a nonradiative site.
TL;DR: In this article, the surface properties of colloidal α-, β- and γ-ferric oxide hydroxides [Fe(O)OH], which were synthesized and aged in this laboratory, have been studied.
Abstract: Fourier-transform infrared spectra and surface properties of colloidal α-, β- and γ-ferric oxide hydroxides [Fe(O)OH], which were synthesized and aged in this laboratory, have been studied. The spectrum of the α phase has a strong absorption band at 3150 cm–1 and two weak ones at 3485 and 3661 cm–1. That of the β phase has a strong band at 3480 cm–1, a weak band at 3659 cm–1 and two very weak bands at 3686 and 3723 cm–1. That of the γ phase has a strong band at 3160 cm–1, a weak band at 3624 cm–1 and a very weak band at 3528 cm–1. The changes of these bands by the adsorption of heavy water, water and methyl iodide molecules and cupric ions have been studied in detail and the various bands were assigned to various OH groups with respect to the crystal structures of these materials.
TL;DR: Transmission electron microscopy of a hydrated interplanetary dust particle (IDP) indicates that it contains abundant magnesium-iron carbonates, primarily breunnerite and magnesian siderite, suggesting that carbonate also may occur in interstellar dust and be the source of the controversial 6.8-micrometer feature from the protostellar spectra.
Abstract: Transmission electron microscopy of a hydrated interplanetary dust particle (IDP) indicates that it contains abundant magnesium-iron carbonates, primarily breunnerite and magnesian siderite. This IDP displays a strong absorption band at 6.8 micrometers in its infrared spectrum, similar to that in certain protostellar spectra. The carbonates probably account for the 6.8-micrometer band in the IDP spectrum, suggesting that carbonate also may occur in interstellar dust and be the source of the controversial 6.8-micrometer feature from the protostellar spectra.
TL;DR: In this paper, the energy transfer process for the general composition GdX3:S,A is discussed in terms of crystal structure, the gadolinium concentration and the interaction mechanism.
Abstract: By suitable sensitization and activation it is possible to design compositions on the basis of gadolinium compounds which show extremely efficient luminescence. For the general composition GdX3:S,A the relevant energy transfer processes are sensitization (S → Gd), energy migration {(Gd → Gd)nx} and trapping (Gd → A). Several examples will be presented in which S → Gd is an efficient process, whereas in other cases it is not. The energy migration process will be discussed in terms of crystal structure, the gadolinium concentration and the interaction mechanism. Finally the trapping process will be discussed. Efficient trapping is possible if the Gd3+ emission lines overlap with a broad allowed absorption band of the activator.
TL;DR: In this paper, a detailed characterization of the microstructure of polysilanes was performed using several different NMR techniques while observing the 29Si, 13C, and proton nucleimore.
Abstract: The recent discovery of soluble organosilane high polymers (1 to 4) has generated significant interest in the properties and applications of these materials. Of particular note is the intense uv absorption at 300 to 380 nm both in solution (5) and in the solid state (6). This unexpected absorption property is attributed to a delocalized sigma > sigma* or sigma > 3dpi transition. It has been demonstrated (5a) that the position of the absorption band (lambda max) as well as the absorptivity per Si-Si bond increases with increasing chain length, reaching a maximum value when the chain becomes very long. In addition, it is found that certain polysilanes exhibit a sharp transition in the uv absorption spectrum at low temperatures for dilute solutions (5b) and at the melt in the case of poly(di-n-hexyl silane) (6). Both of these bathychromic shifts have been attributed to the onset of highly ordered conformations at particular temperatures (5b,5c,6). In an effort to better understand the solution and solid state properties of the polysilanes we have conducted a study to establish a detailed characterization of the microstructure for several polymers. We have applied several different NMR techniques while observing the 29Si, 13C, and proton nucleimore » and report here the results of these measurements. 8 refs., 4 figs.« less
TL;DR: A transmittance model is described which gives results that agree well with the measurements of the atmospheric absorption in the oxygen A-band and is used to investigate the possible extension of the technique to a satellite-borne instrument for estimating surface pressure.
Abstract: A simple technique is described that measures the atmospheric absorption in the oxygen A-band near 0.76 μm. A narrow interference filter is tilted so that its passband scans through the two branches of the absorption band. By viewing the direct solar beam a differential absorption measurement of the mass of oxygen in the optical path is obtained which is then compared to surface pressure. A transmittance model is described which gives results that agree well with the measurements. The model is also used to investigate the possible extension of the technique to a satellite-borne instrument for estimating surface pressure.
TL;DR: In this paper, the optical properties of H2-reduced LiNbO3 have been studied and an absorption band centred at about 2.48 eV is assigned to small polarons.
Abstract: Optical characteristics of H2-reduced LiNbO3 have been studied. The optical transmission in the spectral range 0.3 to 5 mu m is progressively narrowed as the sample is reduced. An absorption band centred at about 2.48 eV is assigned to small polarons. This interpretation is consistent with the published defect structure, transport and spectroscopic reports on reduced LiNbO3. A semi-quantitative analysis of the 2.48 eV absorption band is carried out by employing the Reik and Heese theory (1967) for optical properties of small polarons.
TL;DR: The adsorption of pyridine at room temperature on MgO, CaO, and SrO pre-outgassed at 1073 K gives rise to strong absorption bands in the near-UV and visible between 40,000 and 10,000 cm−1.
TL;DR: A pigment-protein complex containing a reaction center and the B875 light-harvesting complex from Rhodopseudomonas palustris was purified and crystallized in the presence of detergent as discussed by the authors.
TL;DR: In this paper, the authors investigated the solvatochromic absorption band of betaines (N-hydroxyphenyl-pyridinium ions) in the visible and near-infrared regions, which involves substantial electronic charge rearrangement, analogous to intramolecular electron transfer.
TL;DR: In this paper, the response of the EL2 absorption band to monochromatic secondary illumination has been studied in undoped semi-insulating GaAs and shown that photoinduced changes of the absorption band are spectrally nonuniform.
Abstract: The response of the EL2 absorption band to monochromatic secondary illumination has been studied in undoped semi‐insulating GaAs. Photoinduced changes of the absorption band are spectrally nonuniform. In addition, the changes are nonmonotonic in time similar to the EL2 photocapacitance transients: A fast enhancement in absorption is followed by a slow quenching. These data can be explained in terms of the EL2 properties known from photocapacitance studies. A comparison with recent electron paramagnetic resonance (EPR) results for the AsGa antisite provides direct evidence that the EL2 absorption band and the As+Ga EPR are induced by the same defect.
TL;DR: In this article, the Xe-Cl 2 van der Waals complex formed in a supersonic expansion is excited in a two-photon process and the reaction spectra (excitation of the complex and detection of XeCl (B→X) and (C→A) fluorescence) are obtained in the region 290-310 nm.
TL;DR: In this article, the authors show that the most intense luminescence band originates at 2.145 eV and the strong vibronic sideband is mainly due to coupling to a dominant phonon of 30 meV with a Huang-Rhys factor of 9.9.
Abstract: The red luminescence band that occurs in brown diamonds, where the yellow luminescence band originated at 2.721 eV is also present, is excited by light of 450-550 nm, corresponding to an absorption band present in these diamonds. It is a very structured band, up to 12 zero-phonon lines being identified in a 114 meV interval. The authors show that the most intense luminescence band originates at 2.145 eV and the strong vibronic sideband is mainly due to coupling to a dominant phonon of 30 meV with a Huang-Rhys factor of 9.9. Some other zero-phonon lines are also origins of 30 meV phonon progressions. No correlation of line intensities is found from sample to sample or upon varying excitation energy.
TL;DR: In this article, the optical absorption edges of diluted magnetic semiconductors Zn1-xMnxSe have been measured under hydrostatic pressure for x ≦ 0.15 and 0.25.
TL;DR: In this paper, the authors applied far infrared Fourier transform spectroscopy (FFT) to study residual shallow acceptors in semi-insulating GaAs to create a nonequilibrium hole population to neutralize the acceptors.
Abstract: Far‐infrared Fourier transform spectroscopy has been applied to study residual shallow acceptors in as‐grown semi‐insulating GaAs. Secondary optical excitation into the EL2 absorption band has been used to create a nonequilibrium hole population to neutralize the acceptors. Optically induced absorption spectra from carbon and zinc acceptors have been observed. The dependence of these spectra on the secondary illumination is studied. A comparison is made with electronic Raman spectra recorded from the same samples.