Showing papers on "Absorption spectroscopy published in 1989"
IBM1
TL;DR: In this article, the optical absorption spectrum of single dopant molecules of pentacene in a p-terphenyl host crystal at liquid-helium temperatures was observed using two different double-modulation techniques.
Abstract: Using two different double-modulation techniques, we have observed the optical-absorption spectrum of single dopant molecules of pentacene in a p-terphenyl host crystal at liquid-helium temperatures. To achieve this, frequency-modulation spectroscopy was combined either with Stark or ultrasonic modulation to remove interfering background signals from residual amplitude modulation, and the number of molecules in resonance was reduced to one by operating in the wings of the inhomogeneous line. Triplet bottleneck saturation appears to be suppressed in the single-molecule regime.
1,108 citations
TL;DR: In this paper, a model was developed to resolve in situ phytoplankton absorption from a measured in situ total absorption spectrum which includes water, dissolved organics, particulate detritus, and phyto-worms, and was tested on a set of absorption spectra obtained from the productive waters around the San Juan Islands, Washington.
Abstract: Dissolved and suspended materials in the ocean modify the in-water light field by absorbing and scattering photons. Direct measurement of inherent optical properties of individual optical constituents is difficult since the constituents themselves cannot all be separated. A model was developed to resolve in situ phytoplankton absorption from a measured in situ total absorption spectrum which includes water, dissolved organics, particulate detritus, and phytoplankton. The model was tested on a set of absorption spectra obtained from the productive waters around the San Juan Islands, Washington. Results indicate that the model can predict the spectral shape of phytoplankton absorption (rz > 0.9) and total photon absorption by phytoplankton with ~27% error. Total photon absorption can be used to estimate phytoplankton absorption of light energy for improved primary production predictions, given submarine light field measurements or model calculations. Although developed for high chlorophyll waters, the model parameters are easily modified for vario&Casc 1 optical domains.
442 citations
TL;DR: In this paper, the authors measured reflection, luminescence and absorption spectra in an exciton region of (C 10 H 21 NH 3 ) 2 PbI 4, which is determined to be of layered perovskite type by X-ray diffraction.
355 citations
TL;DR: In this paper, a spin-cast analysis of polyaniline in dilute solution in concentrated sulfuric acid and in the form of spincast films is presented, where the results from samples with different molecular weights and with different degrees of protonation are compared.
350 citations
TL;DR: In this paper, the electron energy loss and X-ray absorption spectra of two phases of titanium dioxide-rutile and anatase-were reported, and the authors proposed an interpretation of the Ti L2.3 edge, notably for the presence of a previously unobserved splitting on the L3 edge.
Abstract: The electron energy loss and X-ray absorption spectra of two phases of titanium dioxide-rutile and anatase-are reported. Although the nearest-neighbour environments of titanium and oxygen in both these structures are very similar, noticeable differences are observed between the electron energy loss and the X-ray absorption spectra. Attempts to model these differences using real-space multiple-scattering calculations are reasonably successful at the Ti K and O K edges. The authors propose an interpretation of the Ti L2.3 edge, notably for the presence of a previously unobserved splitting on the L3 edge.
311 citations
TL;DR: In this article, the resonance Raman spectrum of CdSe clusters was measured and the incident photons were resonant with the HOMO-LUMO transition in the clusters, and the strength of the coupling between the lowest electronic excited state and the LO vibration was found to be 20 times weaker in these clusters than in the bulk solid.
Abstract: The resonance Raman spectrum of 45(+−3) A diameter CdSe clusters was measured. The incident photons were resonant with the HOMO–LUMO transition in the clusters. At low temperature, one mode at 205 cm−1 is observed, as well as two overtones, with the integrated areas under these peaks in the ratio of 9:3:1. This mode is assigned as the longest wavelength longitudinal optical vibration of the cluster. The strength of the coupling between the lowest electronic excited state and the LO vibration is found to be 20 times weaker in these clusters than in the bulk solid. The CdSe cluster resonance Raman spectrum is shown to be consistent with the recently measured homogeneous cluster absorption spectrum.
245 citations
TL;DR: In this paper, the authors report on the performance of a newly constructed synchrotron radiation soft x-ray beamline, dubbed Dragon, which is a spherical version of the cylindrical element monochromator design proposed previously.
Abstract: We report on the performance of a newly constructed synchrotron radiation soft x‐ray beamline. This beamline, dubbed Dragon, is a spherical version of the cylindrical element monochromator design proposed previously. By measuring the K‐edge absorption spectra of condensed nitrogen, it is determined that this monochromator has achieved resolving power 104 at 400‐eV photon energy, using its full 15 by 1 mrad angular acceptance. The ideas and advantages contained in the CEM design have also been experimentally confirmed.
245 citations
TL;DR: In this article, the utility of sulfur K-edge X-ray absorption spectroscopy for the determination and quantification of sulfur forms in petroleum asphaltenes has been investigated and the results represent the first demonstration that nonvolatile sulfur forms can be distinguished and approximately quantified by direct measurement.
Abstract: The utility of sulfur K-edge X-ray absorption spectroscopy for the determination and quantification of sulfur forms in petroleum asphaltenes has been investigated. Both X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra were obtained for a selected group of model compounds and for several petroleum asphaltene samples. For the model compounds the sulfur XANES was found to vary widely from compound to compound and to provide a fingerprint for the form of sulfur involved. The use of third derivatives of the spectra enabled discrimination of mixtures of sulfidic and thiophenic model compounds and allowed approximate quantification of the amount of each component in the mixtures and in the asphaltene samples. These results represent the first demonstration that nonvolatile sulfur forms can be distinguished and approximately quantified by direct measurement.
244 citations
TL;DR: In this article, a 6 fs optical pulse was used to impulsively excited the entire manifold of Franck-Condon-connected vibronic levels for the S 0 to S 1 transition in an organic dye in solution.
243 citations
TL;DR: In this paper, the electronic and electrochemical properties of poly(p−phenylene vinylene), poly(thienylene vinylenes), and their derivatives with electron donating moieties such as methyl, methoxy, and ethoxy are studied using the newly developed electrochemical potential spectroscopy (ECPS) and optical spectrum analysis.
Abstract: The electronic and electrochemical properties of poly(p‐phenylene vinylene), poly(thienylene vinylene), and their derivatives with electron donating moieties such as methyl, methoxy, and ethoxy are studied using the newly developed electrochemical potential spectroscopy (ECPS) and optical spectroscopy. It is shown that electrochemically derived band gaps agree well with band gap values obtained from optical measurements. Substitution with electron donating groups substantially lowers the ionization potentials and band gaps. A similar effect can be attributed to the incorporation of a vinylene linkage between rings of the polymer backbone. Our results imply that through a proper choice of substituents and backbone structure one can adjust the electrochemical potentials over a wide range as well as red shift the absorption edge of these polymers. In the case of the alkoxythienylene vinylenes the absorption edge is shifted through the visible range of the spectrum into the near infrared (NIR) yielding polyme...
TL;DR: In this paper, the authors present initial data from x-ray diffraction, ultraviolet-visible (UV-VIS) absorption, and infrared (IR) absorption spectroscopy measurements made during thermal cycling of unoriented, solution cast, poly(3-hexylthiophene) films.
TL;DR: In this article, low-resolution spectra have been obtained for a selection of infrared protostars and one object located behind the Taurus dark cloud and most of the differences in the spectra can be attributed to different H2O ice temperatures combined with additional broad absorption between 3.3 and 3.5 microns plus another absorption in the 2.8-2.9 micron range.
Abstract: Low-resolution spectra have been obtained for a selection of infrared protostars and one object located behind the Taurus dark cloud. Most of the differences in the spectra can be attributed to different H2O ice temperatures combined with additional broad absorption between 3.3 and 3.5 microns plus another absorption in the 2.8-2.9 micron range. An NH3-H2O ice mixture, scattering by H2O ice-coated grains, and hydrated silicates are ruled out as explanations for the last type of absorption. The most plausible explanation is still some form of hydrocarbon in the grain mantles.
TL;DR: In this paper, the effects of compression on the structure and bonding of Mg(OH)2 brucite and Ca(OH2 portlandite are documented to pressures of 34 and 24 GPa, respectively, by way of infrared spectroscopy of the O-H stretching vibration at 300 K.
Abstract: The effects of compression on the structure and bonding of Mg(OH)2 brucite and Ca(OH)2 portlandite are documented to pressures of 34 and 24 GPa, respectively, by way of infrared spectroscopy of the O–H stretching vibration at 300 K. The frequency of the infrared‐active (A2u) mode of both hydroxides decreases with pressure, by −0.6 cm−1/GPa for Mg(OH)2 over the pressure range studied, and by −3.5 cm−1/GPa for Ca(OH)2 to 10.6 GPa. An additional mode observed in Mg(OH)2 is due to an optically induced hot band (A2u X A2u overtone): with increasing pressure, its intensity grows and its frequency decreases (−3.7 cm−1/GPa). The negative pressure dependencies of these modes (negative Gruneisen parameters) are explained in terms of compression increasing the hydrogen bond strength within the hydroxide structure. On increasing pressure above 12.8 GPa, the full width at half‐maximum of the O–H vibration in Ca(OH)2 rapidly broadens by a factor of 4. The infrared data suggest that Ca(OH)2 undergoes pressure‐induced am...
TL;DR: In this paper, an absorption spectrum containing both the XANES and the EXAFS region can be recorded in several seconds if x-ray monochromators at synchrotron beamlines are scanned continuously.
Abstract: An absorption spectrum containing both the XANES and the EXAFS region can be recorded in several seconds if x‐ray monochromators at synchrotron beamlines are scanned continuously. The experimental setups are described in detail. The accuracy of the method up to photon energies of 19 keV is demonstrated. Due to its advantages, the proposed approach may be used as an alternative to the energy dispersive EXAFS method, especially in the case of XANES spectroscopy.
TL;DR: In this paper, a simple structural model for a C:H which is consistent with these results and requires no sp3 bonding is proposed, and the optical gap decreases with increasing bias voltage only up to the onset of sputtering, where the gap sharply increases.
Abstract: The Raman and infrared absorption spectra, optical gaps, and electron spin densities of amorphous carbon films deposited from hydrocarbon plasmas have been systematically studied as a function of deposition conditions and Raman probe wavelength. Although all other probes are consistent with a monotonic increase in intermediate‐range order with substrate bias voltage Vb, the optical gap decreases with increasing Vb (consistent with increasing graphitic domain size) only up to the onset of sputtering, where the gap sharply increases. We propose a simple structural model for a‐C:H which is consistent with these results and requires no sp3 bonding.
TL;DR: In this article, a time dependent method for solving the Schrodinger equation was used to calculate the photon absorption cross section for the photodissociation of a model H+3 system.
Abstract: We use a time dependent method for solving the Schrodinger equation to calculate the photon absorption cross section for the photodissociation of a model H+3 system. The coupling V between the excited states is found to alter the absorption cross section if the time scale ℏ/V is less than the dissociation time. The influence of the relative orientation of the transition dipoles, on the absorption spectrum, is also investigated.
TL;DR: Two-photon absorption of light with nonclassical (squeezed) fluctuations is considered and Mollow' derived the following expression for the twophoton absorption rate from a stationary field through second order in perturbation theory.
Abstract: Two-photon absorption of light with nonclassical (squeezed) fluctuations is considered. Several unique effects are predicted for various possible regimes. These include a linear (instead of quadratic) growth of the absorption rate with the light intensity for weak fields, the possibility of a decreasing absorption with increasing intensity, and orders-or-magnitude differences between absorption rates for phase- and amplitude-squeezed beams of the same intensity.
TL;DR: The optical data indicate that the insulator-to-metal transition in xenon occurs at 132(5) GPa.
Abstract: Xe has been compressed in a diamond-anvil cell to approximately 200 GPa. The metallization of Xe by band-gap closure was investigated by obtaining optical data in both the metallic and insulating states. In the metallic state, the pressure dependence of the plasma frequency was determined from absorption data fitted with a free-electron model. In the insulating state, the pressure dependence of the band gap was determined from absorption data fitted with an indirect-band-gap model. The optical data indicate that the insulator-to-metal transition in Xe occurs at 132(5) GPa.
TL;DR: The line shape of the plasma resonance in both neutral and charged small sodium clusters is calculated and a single peak is predicted that carries most of the oscillator strength.
Abstract: The line shape of the plasma resonance in both neutral and charged small sodium clusters is calculated. The overall properties of the multipeak structure observed in the photoabsorption cross section of spherical ${\mathrm{Na}}_{8}$ and ${\mathrm{Na}}_{20}$ neutral clusters can be understood in terms of Landau damping. Quantal configurations are shown to play an important role. In the case of charged ${\mathrm{Na}}_{9}^{+}$ and ${\mathrm{Na}}_{21}^{+}$ clusters a single peak is predicted that carries most of the oscillator strength.
TL;DR: The third-order optical susceptibility of the Pt, Pb, and metal-free tetrakis(cumylphenoxy)phthalocyanines was measured by degenerate four-wave mixing at 1.064 μm, far from strong absorption bands.
Abstract: The third‐order optical susceptibility of the Pt, Pb, and metal‐free tetrakis(cumylphenoxy)phthalocyanines was measured by degenerate four‐wave mixing at 1.064 μm, far from strong absorption bands. Metal substitution strongly enhances the off‐resonant χ(3). The χ(3)xxxx for Pt‐phthalocyanine (2×10−10 esu) and Pb phthalocyanine (2×10−11esu) is about 45 times and 5 times that of the metal‐free form (4×10−12 esu), respectively.
TL;DR: In this paper, the A 2Pi-X 2Sigma(+) (1,O) and (2, O) bands of the red system were compared with observations of the violet system for one line of sight.
Abstract: Optical absorption-line techniques have been applied to the study of a number of translucent molecular clouds in which the total column densities are large enough that substantial molecular abundances can be maintained. Results are presented for a survey of absorption lines of interstellar C2, CH, and CN. Detections of CN through the A 2Pi-X 2Sigma(+) (1,O) and (2,O) bands of the red system are reported and compared with observations of the violet system for one line of sight. The population distributions in C2 provide diagnostic information on temperature and density. The measured column densities of the three species can be used to test details of the theory of molecule formation in clouds where photoprocesses still play a significant role. The C2 and CH column densities are strongly correlated with each other and probably also with the H2 column density. In contrast, the CN column densities are found to vary greatly from cloud to cloud. The observations are discussed with reference to detailed theoretical models.
TL;DR: In this paper, the Hall effect and the strength of localized vibrational modes (LVM) of silicon impurities using both Fourier transform absorption spectroscopy and Raman scattering at an excitation energy of 3 eV close to the E1 band gap were investigated.
Abstract: n‐type silicon‐doped epitaxial layers of gallium arsenide grown by molecular‐beam epitaxy (MBE) or metal‐organo chemical vapor deposition (MOCVD) have been investigated by measurements of the Hall effect and the strengths of the localized vibrational modes (LVM) of silicon impurities using both Fourier transform absorption spectroscopy and Raman scattering at an excitation energy of 3 eV close to the E1 band gap. Lines from Si(Ga) donors, Si(As) acceptors, Si(Ga)‐Si(As) pairs, and Si‐X, a complex of silicon with a native defect, were detected and correlated for the two techniques. The maximum carrier concentration [n] found for samples grown under standard conditions was 5.5×1018 cm−3. At higher doping levels Si‐X becomes dominant and acts as an acceptor, so reducing [n]. An integrated absorption of 1 cm−2 in the Si(Ga) LVM line corresponds to 5.0±4×1016 atoms cm−3: a similar calibration applies to the Si(As) line, but for Si‐X, an absorption of 1 cm−2 corresponds to only 2.7±1.0×1016 defects cm−3. Possib...
TL;DR: Theoretical estimates of the absorption spectra of collisional pairs of hydrogen and helium (H2-He) are given in this article, with a range of temperatures from 18 to 7000 K. The resulting spectra, which can be computed in seconds even on small computers, are in close agreement with presently known laboratory measurements and extrapolate these dependably to higher as well as to lower temperatures, and to higher frequencies.
Abstract: Theoretical estimates are given of the absorption spectra of collisional pairs of hydrogen and helium (H2-He). The range of temperatures considered is from 18 to 7000 K. The resulting spectra, which can be computed in seconds even on small computers, are in close agreement with presently known laboratory measurements and extrapolate these dependably to higher as well as to lower temperatures, and to higher frequencies. This work is of interest for the modeling of the atmospheres of the outer planets and certain cool stars that contain neutral molecular hydrogen and helium in the near-IR region of the spectrum. 38 references.
TL;DR: In this article, the ultrafast photodynamics of four-coordinate nickel(II) porphyrins in noncoordinating solvents were studied using femtosecond time resolved optical spectroscopy.
Abstract: The ultrafast photodynamics of four‐coordinate nickel(II) porphyrins in noncoordinating solvents has been studied using femtosecond time resolved optical spectroscopy. Unambiguous evidence has been found for the formation of a metastable metal (d,d) excited state in less than 350 fs following excitation of the macrocycle. However, the transient absorption spectrum of this ligand‐field electronic excited state continues to evolve and reaches the steady‐state form only after about 20 ps. This spectral behavior and the attendant complex kinetics can be modeled phenomenologically in terms of a broad distribution of the (d,d) excited states evolving to a narrower distribution. The dynamics are associated with vibrational relaxation. Intramolecular and intermolecular contributions to this process are considered.
TL;DR: In this article, the electronic absorption and emission spectra of seven (Donor)-Acceptor systems are studied with the general structure D-bridge-A, where the bridge consists of an extended, rigid, saturated hydrocarbon skeleton that separates D and A by distances ranging from 3 to 12 CC σ-bonds.
Book•
01 Jan 1989
TL;DR: In this article, the authors used FTIR spectroscopy of molecular orientation in monomolecular layers of polymers on solid substrates to measure the structure and interactions measured by electronic excitation transport.
Abstract: FTIR-spectroscopy of polymers (J.L. Koenig). Studies by FTIR spectroscopy of molecular orientation in monomolecular layers of polymers on solid substrates (T. Arndt, G. Wegner). Glass dynamics probed by motional line narrowing of reactions in polymers via absorption spectroscopy of photochromism (R. Richert). Photoelectron spectroscopy of polymers (K. Seki). Site-selective fluorescence spectroscopy of polymers (H. Bassler). Triplet state spectroscopy of polymers (R.D. Burkhart). Polymers in solids: structure and interactions measured by electronic excitation transport (K.A. Peterson et al.). Nonlinear optical spectroscopy of polymers (E. Cavicchi et al.). Resonance Raman spectroscopy of conjugated polymers (D.N. Batchelder). Brillouin spectroscopy and its application to polymers (J.H. Kruger). Photon correlation spectroscopy of amorphous bulk polymers and compatible polymer blends (G. Meier, G. Fytas). Synchrotron radiation X-ray scattering (M.H.J. Koch). Subject Index.
TL;DR: In this article, the van der Waals vibrations of aniline, phenol, fluorobenzene, chlorobenzenes, phenols, and anilines were measured using one-color resonance enhanced multiphoton ionization spectroscopy, together with time-of-flight mass spectrometry.
Abstract: The van der Waals vibrations of aniline–, phenol–, fluorobenzene–, and chlorobenzene–Ar1 complexes have been measured using one‐color resonance enhanced multiphoton ionization spectroscopy, together with time‐of‐flight mass spectrometry, in a skimmed supersonic molecular beam. A delayed ionization extraction technique is used to suppress contributions to the spectra from dissociating complexes. The S1–S0 electronic origins for the van der Waals complexes are found to be shifted towards lower energy (red shift) relative to the parent molecule electronic origin for all the Ar1 complexes. The red shifts increase in magnitude in the order: fluorobenzene, chlorobenzene, phenol, aniline. Progressions, overtones and combination transitions involving the low frequency van der Waals vibrations, i.e., the symmetric bend (bx), the asymmetric bend (by) and the stretch (sz) are observed clearly in the S1←S0 excitation spectra. Intensity profiles are found to deviate substantially from those expected on the basis of ha...
TL;DR: In this article, transient optical absorption spectroscopy has been used for the first time to study the transport of ground state Y, Ba, Cu, and Ba+ following excimer laser ablation of Y1Ba2Cu3O7−x pellets.
Abstract: Transient optical absorption spectroscopy has been utilized for the first time to study the transport of ground‐state Y, Ba, Cu, and Ba+ following excimer laser ablation of Y1Ba2Cu3O7−x pellets. Spectral broadening of the atomic lines monitored in both absorption and emission is reported, indicating the existence of gas phase collisions in the plume of ejected material. Time‐of‐flight velocity distributions of the nonemitting neutrals and ions determined by the absorption technique are broadened and shifted to lower velocities than the velocity distributions inferred from excited‐state fluorescence in the plume. Absorption by ground‐state Y+, YO, BaO, and CuO also has been observed with this technique. The absorption technique, and its application as an in situ monitor of neutral and ion transport during deposition of superconducting thin films, is described.
TL;DR: In this article, the effect of heteroatom composition and film growth conditions on the redox and optical properties of the copolymers is discussed, and a qualitative energy level diagram is presented.