Showing papers on "Absorption spectroscopy published in 1985"

First observation of an extremely large‐dipole infrared transition within the conduction band of a GaAs quantum well

Abstract: A new type of optical transition in GaAs quantum wells has been observed. The dipole occurs between two envelope states of the conduction‐band electron wave function, and is called a quantum well envelope state transition (QWEST). The QWEST is observed by infrared absorption for two structures with 65‐A‐thick‐ and 82‐A‐thick wells. The transitions exhibit resonant energies of 152 and 121 meV respectively, full width at half‐maximum linewidths as narrow as 10 meV at room temperature, and an oscillator strength of 12.2. The material is anticipated to have subpicosecond relaxation times and be ideal for low‐power optical digital logic.

3d x-ray-absorption lines and the 3d94fn+1 multiplets of the lanthanides.

Abstract: We have measured and calculated the 3d (${M}_{4}$,5) absorption spectra for all the rare-earth metals, as well as the full 3${d}^{9}$4${f}^{n+1}$ multiplets for the early and late rare earths. The quality of agreement between theory and experiment is excellent, except for Sm. In x-ray-absorption spectroscopy (XAS), only dipole selected lines are seen but all multiplet effects can be observed in x-ray photoemission spectroscopy. The line shapes and 3d-4f interactions are discussed. Our results provide an improved basis for use of the 3d XAS spectra for studies of ``mixed-valence'' systems.

Phenomena Induced by Intermolecular Interactions

Abstract: Section 1: Compressed Gases and the Effect of Density.- A. Far Infrared and Infrared Absorption.- Classical Multipole Models: Comparison with Ab Initio and Experimental Results.- Ab Initio Calculations of Collision Induced Dipole Moments.- A Comparative Study of the Dielectric, Refractive and Kerr Virial Coefficients.- The Infrared and Raman Line Shapes of Pairs of Interacting Molecules.- Collision-Induced Absorption in the Microwave Region.- Collision-Induced Absorption in N2 at Various Temperatures.- Far Infrared Absorption Spectra in Gaseous Methane from 138 to 296 K.- Induced Vibrational Absorption in the Hydrogens.- Simultaneous Transitions in Compressed Gas Mixtures.- Molecular Motions in Dense Fluids from Induced Rotational Spectra.- Intercollisional Interference - Theory and Experiment.- Workshop Report: Infrared Absorption in Compressed Gases.- B. Light Scattering.- Ab Initio and Approximate Calcuations of Collision-Induced Polarizabilities.- Depolarization Ratio of Light Scattered by a Gas of Isotropic Molecules.- Depolarized Interaction Induced Light Scattering Experiments in Argon, Krypton, Xenon.- Interaction Induced Rotational Light Scattering in Molecular Gases.- Workshop Report: Light Scattering in Compressed Gases.- Section 2: Liquids and Liquid State Interactions.- A. Atomic Systems.- Theory of Collision-Induced Light Scattering and Absorption in Dense Rare Gas Fluids.- Calculation of Spectral Moments for Induced Absorption in Liquids.- B. Molecular Systems.- Interaction-Induced Vibrational Spectra in Liquids.- Far Infrared Induced Absorption in Highly Compressed Atomic and Molecular Systems.- Theoretical Interpretation of the Far Infrared Absorption Spectrum in Molecular Liquids: Nitrogen.- Molecular Dynamics Studies of Interaction Induced Absorption and Light Scattering in Diatomic Systems.- Interaction Induced Light Scattering from Tetrahedral Molecules.- Local Fields in Liquids.- Pressure - An Essential Experimental Variable in Spectroscopic Studies of Liquids.- Workshop Report: Liquids and Liquid State Interactions.- Section 3: Solid State, Amorphous, and Ionic Systems.- Study of the Collective Excitations in H2 as Observed in Far Infrared Absorption.- Induced Light Scattering in Disordered Solids.- Infrared Induced Absorption of Nitrogen and Methane Adsorbed in NaA Synthetic Zeolite.- Charge Induced Effects in Solid Tritium and Deuterium.- Workshop Reports: Some Considerations on Spectra Induced by Intermolecular Interactions in Molecular Solids and Amorphous Systems.- Section 4: Induced Transitions in Allowed Spectra.- Collision-Induced Effects in Allowed Infrared and Raman Spectra of Molecular Fluids.- Raman Scattering from Linear Molecules.- The Interference of Molecular and Interaction-Induced Effects in Liquids.- Interaction Induced Spectra of "Large" Molecules in Liquids.- The Infrared Spectrum of HD.- Workshop Report: The Interference of Induced and Allowed Molecular Moments in Liquids.- Section 5: Related Subjects.- Contribution of Bound Dimers, (N2)2, to the Interaction Induced Infrared Spectrum of Nitrogen.- Vibrational Spectral Lineshapes of Charge Transfer Complexes.- Collision-Induced Effects in Planetary Atmospheres.- Time-Domain Separation of Collision Induced and Allowed Raman Spectra.- Collision-Induced Radiative Transitions at Optical Frequencies.- Comments on Hyper-Rayleigh Scattering.- Comments on the Spectra of the Halogens and Halogen Complexes in Solution.- Author index.- Chemical index.

Fabrication of low-loss optical fibres containing rare-earth ions

Abstract: Fibres containing rare-earth ions have been produced by an extended MCVD process. The fibres have very high absorption levels in the visible and near infra-red regions, without significantly compromising the low-loss characteristics of the fibre at wavelengths between 950 and 1400 nm.

The infrared predissociation spectra of water clusters

Abstract: Infrared predissociation spectra of water clusters have been measured in the frequency range 3000–3800 cm−1 using a molecular beam–color center laser apparatus. The transition from a spectrum resembling that of liquid water to that of the dimer is clearly seen. Detailed theoretical analyses using normal mode theory, local mode theory, and a quantum simulation method are used to interpret the spectrum in terms of a potential surface that includes both intramolecular and intermolecular degrees of freedom.

Photostimulated Luminescence (PSL) and Color Centers in BaFX : Eu2 + ( X = Cl , Br , I ) Phosphors

Abstract: Single crystals of BaFX:Eu/sup 2 +/ phosphors have been prepared. Optical absorption spectra and stimulation spectra measured with polarized light are in good agreement with each other. The experimental ESR spectra of the F-rich and X--rich undoped BaFX powder phosphors which have been x-rayed coincide with the calculated spectra of F(X-) and F(F-) centers, respectively. In addition, the decrease of the ESR signal intensity with light exposure is substantially in agreement with the stimulation spectra for each case. It is concluded that the PSL of BaFX:Eu/sup 2 +/ phosphors is caused by the liberation of electrons trapped at F centers created by the x-ray exposure.

Effects of oxygen content on the optical properties of tantalum oxide films deposited by ion-beam sputtering.

Abstract: Ion-beam sputter deposition of tantalum oxide films was investigated for possible optical coating applications. Optical properties of such films were found to be a sensitive function of oxygen-to-argon ratio in the ion beam. Refractive index and absorption coefficient were determined in the 250–2000-nm wavelength range by spectrophotometric transmissivity. The different bonding states of the tantalum atoms were revealed by x-ray photoelectron spectroscopy. The visible wavelength refractive index was found to be 2.18 and optical band gap 4.3 eV, so long as the films did not contain inclusions of metallic tantalum. Films with an admixture of oxygen deficient suboxide components had a low-energy tail of increasing magnitude in the absorption spectrum.

Observation of a C-1s core exciton in diamond.

Abstract: A well-resolved core exciton at the bulk diamond C-$1s$ absorption edge has been observed using high-resolution partial-yield spectroscopy with synchrotron radiation. The obtained excitonic binding energy, 0.19\ifmmode\pm\else\textpm\fi{}0.015 eV, agrees well with a first-principles effective-mass approximation (EMA). This is in sharp contrast to other semiconductors (Si, Ge, and GaAs) where reported excitonic shifts far exceed EMA estimates. In light of these results, one must question whether previous measurements overestimate the core-hole interaction or if they indicate a breakdown of the EMA for core excitons.

l2,3 absorption-spectra of the lighter 3d transition-metals

Abstract: A theory is presented for the x-ray absorption spectra of materials characterized by bandwidths which are somewhat larger than the (quasiatomic) electron correlation energies. Assuming that an empty-band approximation is appropriate for nearly empty bands we show that the problem is much akin to the well-known Coulomb localization problem in Auger spectroscopy, with an enhanced sensitivity for exchange and multipole effects because of the dipole selection rules. Using first-principles band structure and atomic data as input for the theory, we calculate the spectra of Ca, Ti, and V and obtain good agreement with high-resolution experimental spectra.

Protein Conformation by Infrared Spectroscopy: Resolution Enhancement by Fourier Self-Deconvolution

Abstract: Fourier self-deconvolution (FSD) has been employed to enhance the resolution of the infrared spectra of proteins in the solid state and in D2O solution. The feasibility of using diffuse reflectance spectrometry for measuring the infrared spectra of solid proteins has been demonstrated. FSD permits inherently broad absorption bands to be resolved into distinct peaks which can be associated with specific protein secondary structures. Because the areas of the resolved peaks are the same as the areas of the previously unidentifiable components, this new method should enable quantitative estimates of the proportion of each conformation in a protein to be calculated.

2p absorption-spectra of the 3d elements

Abstract: The near-edge structure of the 2p absorption edges of the complete series of the 3d transition metals has been investigated by high-resolution electron-energy-loss spectroscopy. Structures in the spectra were observed that could not be resolved in previous studies. The data are compared with single-particle calculations of the 2p\ensuremath{\rightarrow}3d transition probability as well as with bremsstrahlung isochromat spectra. The comparison shows that the absorption spectra cannot be described by the density of unoccupied d states even when single-particle matrix-element effects are taken into account. Especially at the beginning of the 3d series, the interaction with the core hole is an important parameter.

Description of the absorption spectrum of iodine recorded by means of Fourier Transform Spectroscopy : the (B-X) system

Abstract: An in extenso analysis of the (B-X) I2 iodine absorption spectrum recorded by means of Fourier Transform Spectroscopy is presented. It is shown that the 100 000 recorded transitions covering the 11 000-20 040 cm-1 range and published in several Atlases may be recalculated by means of only 46 constants : 45 are Dunham coefficients describing the vibrational and rotational constants of both X state (up to v" = 19) and B state (up to v' = 80, situated only at 1.6 cm-1 from the dissociation limit of the B state), and one empirical scaling factor which takes account of neglected centrifugal constants higher than Mv. The overall standard error between computed and measured wavenumbers is equal to 0.002 cm -1 in agreement with the differences of numerous independent absolute wavenumbers and the computed ones.

Structure and dynamics of the excited CH–chromophore in (CF3)3CH

Abstract: The absorption spectra of gaseous (CF3) 3CH (1,1,1,3,3,3‐hexafluoro, 2‐trifluoromethyl propane) were recorded in the IR between 800 and 12 000 cm−1 by high resolution interferometric Fourier transform techniques and in the visible from 12 000 to 17 000 cm−1 by laser photoacoustic spectroscopy. Instead of single bands in the CH overtone region, complex multiplet structures were observed. Thirty‐nine bands were assigned as arising from the interacting CH‐stretching and CH‐bending manifolds, which account for most of the absorption in the overtone region. The results can be understood quantitatively with an effective, tridiagonal many‐level Fermi resonance Hamiltonian. Close agreement is obtained for the positions and intensities of the observed spectral features using only seven spectroscopic parameters. The experimental and theoretical results are summarized in Tables II, III, and IV. The Hamiltonian can be used to calculate and understand the time‐dependent redistribution of vibrational energy between the...

Modeling of pressure-induced far-infrared absorption spectra Molecular hydrogen pairs

Abstract: Meyer et al. (1985) have calculated the accurate induced dipole moment function of H2-H2 from first principles, using highly correlated wave functions for the first time in such work. The present paper is concerned with the collision-induced translational-rotational absorption coefficient for molecular hydrogen pairs, taking into account computations on the basis of the fundamental theory considered by Meyer et al. Data have been obtained for temperatures in the range from 40 to 300 K. Criteria are developed for choosing among various model line shapes. It is found that certain models are capable of approximating the quantum profiles closely, with rms errors of only a few percent.

Collisional energy transfer of vibrationally highly excited molecules. V. UV absorption study of azulene

Abstract: Vibrationally highly excited azulene molecules in the electronic ground state (excitation energy 〈E〉=30 600 cm−1) were produced by excitation with a N2 laser. The stepwise deactivation of the excited molecules in collisions with a variety of 23 inert bath gases was monitored by time‐resolved hot UV absorption spectroscopy at 290 nm. Using previously determined calibration curves of the absorption coefficient at 290 nm as a function of the excitation energy 〈E〉, energy‐loss curves 〈E(t)〉 were recorded and analyzed with respect to the average energies 〈ΔE〉 transferred per collision. The dependencies of 〈ΔE〉 on the excitation energy 〈E〉 were derived. In most cases, 〈ΔE〉 was found to be only weakly dependent on 〈E〉 above 10 000 cm−1, whereas a stronger rise with energy became apparent only at lower energies. A comparison with earlier IR emission experiments on the azulene system is given.

Infrared diode laser spectroscopy of the NO3 ν3 band

Abstract: The N–O degenerate stretching band ν3 of the NO3 radical has been studied in the gas phase by infrared tunable diode laser spectroscopy. The NO3 radical was generated by the reaction of NO2 with an excess of O3. Zeeman modulation was employed to observe the paramagnetic absorption lines of 14NO3 and 15NO3 in the wavelength regions 1480–1500 and 1463–1479 cm−1, respectively. Only K’’=3n (n denoting an integer) transitions were observed, and the N’’=even members were missing from the K’’=0 manifold. These observations indicate that the NO3 radical belongs to D3h symmetry in the 2A2’ ground electronic state. The observed spectrum was analyzed using a symmetric‐top vibration‐rotation Hamiltonian including the spin‐rotation interaction. The main parameters thus obtained for 14NO3 are B3=0.455 22(11), C3=0.227 13(6), Cζ3=0.044 79(11), q3=0.001 624(33), t3= 0.000 000 458 0(43), B0=0.457 46(12), C0=B0/2 (fixed), ebb=0.0280(27), and ecc=0.1197(36) for v3=1, ebb=0.0277(28), and ecc=0.1117(34) for v=0, and ν0=1492.3...

Analysis of optical spectra from single crystals of Rhodopseudomonas viridis reaction centers

Abstract: Absorption spectra and light-induced absorbance changes of crystals from Rhodopseudomonas viridis reaction centers are recorded. A theoretical analysis of the absorption and circular dichroism spectra is presented, yielding a consistent picture of spectroscopic and structural information.