Showing papers on "Absorption spectroscopy published in 1968"

Electronic Energy Levels in the Trivalent Lanthanide Aquo Ions. I. Pr3+, Nd3+, Pm3+, Sm3+, Dy3+, Ho3+, Er3+, and Tm3+

Abstract: The free‐ion energy‐level schemes of the Pr3+, Nd3+, Pm3+, Sm3+, Dy3+, Ho3+, Er3+, and Tm3+ aquo ions have been determined from their absorption spectra in dilute acid solution at 25°. Energy‐level assignments were made by comparison with crystal spectra, and on the basis of correlations between calculated and observed band intensities. For most of the ions, it was possible to identify several transitions giving rise to bands at energies as high as 45 000–50 000 cm−1. Sufficient numbers of assignments were made to justify inclusion of the effects of configuration interaction in the calculation of the energy‐level parameters. Variation of the electrostatic, spin–orbit coupling, and configuration‐interaction parameters across the lanthanide series is examined.

Coherent Averaging Effects in Magnetic Resonance

Abstract: A theory is developed to describe the slow component of the transient decay of transverse spin magnetization, and the central component of the slow-passage absorption spectrum, of a system of spins which is subjected to a periodic and cyclic perturbation. The theory is used to analyze and compare various schemes for high-resolution NMR of solids, including the spinning of the sample about an axis oriented at the "magic angle," the rotating-frame magic-angle experiment of Lee and Goldburg, pulsed versions of the latter, and a number of new pulsed-NMR experiments recently developed in this laboratory. Attention is focused on the factors, both theoretical and practical, which are important in obtaining optimal suppression of static dipole-dipole interactions and quadrupole splittings, and retention of chemical and Knight shifts and scalar spin-spin interactions. Several new experiments are proposed.

Guest-host Interactions in Nematic Liquid Crystals. A New Electro-optic Effect

Abstract: A new electro‐optic effect is presented, based on guest‐host interactions in nematic liquid crystals. The ability of a nematic liquid crystal to cooperatively align in an electric field is used to orient ``guest'' dichroic dye molecules (molecules whose absorption spectrum is a function of the molecular orientation with respect to the polarization of the incident light). Thus one can electrically switch the color of transmitted light using fields of the order of 104 V/cm.

Optical interactions in solids

Abstract: Elements of Quantum Mechanics Elements of Group Theory Connection of Quantum Mechanics with Group Theory The Hydrogen Atom The Complex Atom - Multiplet Theory The Magnetic Ion in a Crystal - The Role of Symmetry The Weak Field Scheme The Medium Field Scheme The Strong Field Scheme Covalent Bonding and Its Effect on Magnetic Ions in Crystals The Quantum Theory of the Radiation Field Molecular Vibrations Lattice Vibrations The Ion-Photon Interaction - Absorption and Emission of Radiation The Ion-Vibration Interaction - Radiationless Processes - Thermal Shift and Broadening of Sharp Lines Vibrational-Electronic Interaction and Spectra Absorption Spectra of Magnetic Ions in Crystals Fluorescence Spectra of Magnetic Ions in Crystals Elements of Laser Theory

Cation Distributions in Octahedral and Tetrahedral Sites of the Ferrimagnetic Spinel CoFe2O4

Abstract: Mossbauer spectra of CoFe2O4 show that this spinel is not completely inverse and that the degree of inversion depends on the heat treatment of the material. The magnetic moments of the slowly cooled and the quenched material are 3.4 and 3.9 μB per unit chemical formula, respectively, and the Neel temperatures are 798°K and 792°K, respectively. From the width and the shape of the absorption lines of the Mossbauer spectra several magnetic hyperfine fields have been identified with different B sites and the temperature dependences of these fields have been determined. The different hyperfine fields have been attributed to 57Fe nuclei in B sites with different ratios of iron and cobalt ions in the six nearest‐neighbor A sites.

Single‐Crystal Spectra of Ferrimyoglobin Complexes in Polarized Light

Abstract: The polarized absorption spectra of ferrimyoglobin cyanide, ammonia, azide, fluoride, formate, and water (acid ferrimyoglobin) complexes in single crystals are described. Special emphasis is placed on the polarization‐ratio (PR) spectrum—the spectrum of the intensity ratio for light absorbed along and perpendicular to the crystal symmetry axis. It is shown that the PR spectrum magnifies spectral effects that are otherwise obscured by wide absorption bands, and it is shown to be a most useful parameter for studying the spectra of those systems that are intrinsically broad and whose spectra do not show any sharpening at low temperature. The results confirm many general features of porphyrin spectra such as the polarization of the B and Q states, the vibronic nature of the Qv state, and the intensity imbalance in the Q0 state. The substances studied span a variety of spectral types, from low‐spin, through mixed‐spin, to high‐spin iron complexes. The high‐spin spectra show, in addition to porphyrin bands, cha...

The absorption spectrum of the free SiH2 radical

Abstract: The absorption spectrum of SiH2 in the visible region has been photographed at high dispersion and the rotational structure of three bands has been analyzed. In the lower electronic state 1A1 the H...

Band Structure and the Titanium LII, III X‐Ray Emission and Absorption Spectra from Pure Metal, Oxides, Nitride, Carbide, and Boride

Abstract: The titanium LII, III x‐ray emission and absorption spectra (λ∼27.5 A) from pure metal, oxides, nitride, carbide, and boride have been investigated using a plane‐crystal vacuum spectrometer with electron‐beam excitation and flow‐proportional counter detection. Emission spectra were studied over a wide range of accelerating voltages and takeoff angles, showing that satellite emission and self‐absorption effects can significantly distort the band shapes and energy positions of intensity maxima. A replica of the LII, III absorption spectrum can be constructed solely from emission spectra affiicted with widely different amounts of self‐absorption. The LII, III emission spectra from the oxides, nitride, and carbide exhibit an important crossover transition from the 2p level of the anion to the LII and LIII levels of titanium. Results indicate formation of a 3d band in titanium compounds which is only partially filled, giving rise to metallic conduction. X‐ray data is compared to density of states calculations ...

Spectroscopic Studies of Ruthenium(II) Complexes. Assignment of the Luminescence

Abstract: Absorption and emission spectra of ruthenium 2 complexes dissolved in rigid glasses, discussing crystal field theory and luminescence

Microwave Spectrum, Conformation, Dipole Moment, and Barrier to Internal Rotation in Methyl Vinyl Ether

Abstract: The microwave spectrum of methyl vinyl ether, CH3OCH=CH2, has been studied in the frequency region 8 to 40 Gc/sec Absorption lines have been assigned to a planar cis isomer, with a barrier to internal rotation of the methyl group of 3830 ± 100 cal/mole The components of the dipole moment along the principal axes of inertia were measured and found to be μa = 0294 D, μb = 0915 D (μ total = 096 D) Spectra were observed of the excited methyl torsional state and of two additional excited vibrational states, corresponding, respectively, to vibrations at about 240, 205, and 327 cm−1 These findings are confirmed by far‐infrared and Raman spectra

Use of Molecular Orbital Theory to Interpret X‐Ray K‐Absorption Spectral Data

Abstract: This paper demonstrates how molecular orbital theory can be useful in obtaining chemical information from x‐ray absorption spectra. Basic molecular orbital theory concepts such as symmetry and overlap of wavefunctions are used to explain the K‐absorption spectra of first‐row transition metal complexes. In x‐ray K‐absorption spectroscopy, 1s electrons are excited to high‐energy unoccupied orbitals; thus, the main absorption maxima (for first row transition metals) are due to excitations to the triply degenerate 4p antibonding orbitals. The shifts in these peaks are due to changes in the orbital energy levels, which, of course, are a function of chemical bonding. A splitting or a broadening of a peak is an indication of a splitting of the degenerate energy levels, which in turn is an indication of unsymmetrical metal to ligand bonding. It is also shown how x‐ray absorption spectra can be useful in determining the lattice sites of atoms of nearly equal x‐ray scattering power.

Vacuum ultraviolet absorption spectra of sublimed films of nucleic acid bases

Abstract: Measurements of the optical absorption spectra of the sublimed films of adenine, guanine, cytosine, thymine, and uracil were extended down to 120 mμ at room temperature. Several remarkable absorption peaks were found to exist below 190 mμ in addition to the already known ones near 260 mμ and 200 mμ. The intensities of these peaks were comparable to or, in some cases, even larger than those near 260 mμ and 200 mμ. It was found that the relative intensities of the absorption peaks differed considerably from sample to sample for all five bases, probably due to variation in the arrangement of the bases in the sublimed films. It was found also that the absorption spectra of the sublimed films change with aging on standing in vacuo at room temperature. On comparing the spectra of several fresh samples it was found that the intensities of the transitions with wavelength longer than 160 mμ of adenine, guanine, and uracil films are inversely correlated with those of the transitions shorter than 160mμ.

Physical properties of a transition metal oxide: optical and photoelectric properties of single crystal and thin film molybdenum trioxide

Abstract: The optical absorption spectra of single crystals and thin films of MoO 3 have been measured in the temperature range 150 to 340 °K with polarized light. At room temperature, the absorption spectrum of a single crystal consists of two peaks at λ 4130 and λ 3930 A with E || C and only one absorption peak at 4250 A with E ⊥ C followed by a rapid rise in absorption. The temperature and frequency dependence of the absorption coefficient in the edge over a range of absorption magnitudes 10 2 -10 5 cm -1 are described by expressions of the form K(v, T) = K 0 exp[— (β/kT) (E 0 — hv )]. The temperature dependence of the absorption edge was found to be linear from 340 to 150 °K with a temperature coefficient of — 6.2 x 10 -4 and — 9.3 x 10 -4 eV/°K for E || C and E ⊥ C , respectively. The corresponding temperature co­efficients in thin films are — 2.7 x 10 -4 and —4.0 x 10 -4 eV/°K for E|| and ⊥ to the film surface, respectively. Measurements have been made of the refractive indices of a single crystal and thin films. Ultraviolet irradiation of a thin film of MoO 3 produces a broad colour centre band having a maximum at 8700 A. Several absorption peaks are resolvable in polarized light. On cooling down to 150 °K, the peak position shifts to shorter wavelength by 400 A (4.67 x 10 -4 eV/°K). An e. s. r. signal with g = 2.001 ± 0.005 has been observed in the colour film. The electrical conductivity has been measured on single crystals and polycrystalline samples in the temperature range 25 to 500 °C, and the activation energies are found to be 1.83 ± 0.01 eV (intrinsic) and 0.29 to 0.70 eV (extrinsic). Photoconductivity has been measured in single crystals and thin films as a function of photon energy, temperature, and irradiation intensity. Trapping plays a significant role in the conduction phenomena. The thermal activation energies associated with different trapping levels were determined from the photoconductive decay curves and the electrical glow peaks measurements and were found to be in the range 0.16 to 0.64 eV.

Multiplet Structure in the Absorption Spectrum of Eu2

Abstract: The Eu2+ ion in alkaline earth fluorides produces two broad absorption bands arising from 4f−5d transitions. The band at 3 eV has a structure with six resolved peaks. This structure is independent of Eu concentration. This band is attributed to transitions from the 4f 7(8 S) ground state to 4f 6(7 FJ ) 5eg , the peaks being associated with the different J values in f 6(7 F). The higher energy band in the fluorides and the absorption band in the europous chalcognides are correspondingly attributed to 4f 6(7 FJ ) 5t 2g states. With this model, with 7 FJ intervals obtained from the resolved structure in the EuF2 data, and from the experimental oscillator strengths of the observed absorption bands, the 4f−5d radial integral is calculated and a consistent set of values of 0.23±0.01 A obtained. The Faraday and Voigt magneto‐optic effects are calculated for EuF2 at 4330 A. The room‐temperature Verdet constant is −7.1 min/Oe·cm as compared with the experimental value of −6.6 min/Oe·cm. The Voigt birefringence at 15°K and 20 kOe is n∥−‐n⊥=−2.0×10−4 while experiment gives −1.7×10−4.

Selective Polarization of Light Due to Absorption by Small Elongated Silver Particles in Glass

Abstract: Polarizing glasses were made by stretching glass containing colloidal silver. The position of the absorption bands depends strongly on the elongation. This dependence seems to be consistent with the predictions of the theory of light absorption by small metal particles based on a free electron model.

Some optical properties of CuPd, AgPd, AuPd and CuMn, AgMn alloys

Abstract: Measurements of the transmission and reflection coefficients have been made on evaporated films of solid solutions of Pd in Cu, Ag and Au and Mn in Cu and Ag. In the ease of the Pd alloys additional absorption attributed to resonant bound states associated with the Pd d electrons has been observed. The location and breadth of these resonant levels have been determined for the Ag and Au alloys. In Cu the resonant state absorption overlaps the Cu absorption edge and is not separable. In the CuMn and AgMn alloys the bound d states of the Mn are known to be spin split. No evidence for the optical absorption due to these states has been found in CuMn which is interpreted as implying a very small splitting energy ∼0·25 ev per spin. Weak absorption is observed in the case of AgMn alloys and this is interpreted as indicating a spin splitting energy of ∼ 1 ev per spin. In all these alloys the absorption spectra of the matrix, particularly the characteristic edges of Cu, Ag and Au, are little affected by t...

Static Crystal Effects on the Vibronic Structure of the Phosphorescence, Fluorescence, and Absorption Spectra of Benzene Isotopic Mixed Crystals

Abstract: The phosphorescence, fluorescence, and absorption spectra of the isotopic benzenes C6H6, C6H5D, p‐C6H4D2, and sym‐C6H3D3, present as dilute guests in a C6D6 host crystal at 4.2°K, are obtained with sufficient spectral resolution to ascertain the magnitude of the crystalline site effects. The relative vibronic intensities in fluorescence and phosphorescence are compared. Two site effects are emphasized: site splitting of degenerate fundamentals and orientational effects. The former can occur for the isotopes C6H6 and sym‐C6H3D3, while the latter is possible only for isotopes with less than a molecular threefold rotation axis. The observations show that both site‐splitting and orientational effects do occur as a general rule on vibronic and vibrational states in benzene isotopic mixed crystals. An empirical correlation between the magnitudes of the site splitting, orientation effect and site (gas‐to‐crystal) shifts for in‐plane and out‐of‐plane modes is noted. The phosphorescence of C6H6 and sym‐C6H3D3 has ...

Absorption of Infrared Radiant Energy by CO 2 and H 2 O. III. Absorption by H 2 O between 0.5 and 36 cm −1 (278 μ−2 cm)*

Abstract: Interferometric techniques have been employed to measure the H2O absorption between approximately 12.6 cm−1 and 36.0 cm−1. The experimental results, along with results obtained between 0.5 cm−1 and 10 cm−1 by other workers, have been compared with calculated values of transmittance based on theoretically determined positions, strengths, widths, and shapes of the absorption lines. From these comparisons it has become apparent that none of the well-known theoretical line shapes are correct for the extreme wings of the H2O lines below approximately 40 cm−1. The amount of continuum absorption which must be added to the theoretical absorption coefficient to provide agreement with the experimental results has been determined for N2- and self-broadened lines. A table of the line parameters has been included, along with a discussion of the procedure to be followed in calculating the transmittance of homogeneous and inhomogeneous paths.

Ultra-violet absorption spectrum of isocyanic acid

Abstract: The absorption spectrum of HNCO between 2000 and 2800 A has been photographed with high resolution and absorption paths of up to 8 m atm. None of the bands are completely sharp, but many show coarse rotational structure. Long progressions of bands are assigned to excitation of an NCO bending vibration. The rotational structure shows that the NCO chain is strongly bent in the excited state, and that either ∠NCO = 119° and rNC+rCO= 2.64 A if the excited state is trans, or ∠NCO = 129° and rNC+rCO= 2.60 A if the excited state is cis. Comparison of the observed band contours with computed asymmetric top band syntheses proves that the bands have type C polarization. The electronic and geometrical structure of HNCO are discussed with the aid of a diagram correlating the molecular orbitals of HABC and AB2 molecules.

Steric structure of L-proline oligopeptides. II. Far-ultraviolet absorption spectra and optical rotations of L-proline oligopeptides.

Abstract: The results of the measurement of the far-ultraviolet absorption spectra of L-proline oligomers in water and acetonitrile are summarized as follows. The monomer has an absorption maximum at 182.5 mμ in acetonitrile. The absorption maximum of the dimer is found at 185 mμ and a shoulder appears around 200 mμ, that is, splitting of the absorption spectrum is observed in the dimer. As the degree of polymerization increases, the position of the shoulder shifts toward the wavelength of the absorption maximum of poly-L-proline II, with an accompanying increase in intensity. We may describe the absorption peak around 203 mμ of poly-L-proline II as identical with the shoulder with an increased intensity. By measurements of optical rotatory dispersion and circular dichroic spectra, it was also confirmed that the appearance of the helical conformation commences at the tetramer. When the number of residues is five or greater, the conformation of the helical structure of poly-L-proline II seems to be completed.

Collisional broadening of CO absorption lines by foreign gases.

Abstract: Collisional line broadening ability of various foreign gases relative to nitrogen for rotational lines in fundamental absorption band of carbon monoxide

Optical Transitions in the Spectra of the Fundamental Absorption and Reflection of InSe Single Crystals

Abstract: The spectrum of the fundamental absorption and reflection of n-type InSe single crystals is studied in the energy region 1 to 5 eV and in the temperature range 293 to 90 °K. In the spectrum an absorption is observed which may be related to direct and indicrect interband transitions. The main parameters characterizing the indirect and direct optical transitions are determined. The fine structure in the absorption spectrum due to excitons is investigated. On the basis of the analysis of the optical absorption and reflection properties in the fundamental region and using selection rules, the character of optical transitions as well as the peculiarities in the energy band structure of InSe single crystals are established. Das Spektrum der Grundgitterabsorption und Reflexion von n-leitenden InSe-Einkristallen wird im Energiebereich 1 bis 5 eV und im Temperaturintervall 293 bis 90 °K untersucht. Im Spektrum wird eine Absorption beobachtet, die direkten und indirekten Interbandubergangen zugeordnet werden kann. Die Hauptparameter fur die indirekten und direkten optischen Ubergange werden bestimmt. Die durch Exzitonen verursachte Feinstruktur des Absorptionsspektrums wird untersucht. Aus der Analyse der optischen Absorptions- und Reflexionseigenschaften im Grundgittergebiet in Zusammenhang mit den Auswahlregeln werden sowohl der Charakter der optischen Ubergange als auch die Besonderheiten der Energiebandstruktur von InSe-Einkristallen festgestellt.

Thermodynamic, ultrasonic, spectroscopic and miscibility studies of water + methyl cyanide solutions

Abstract: The ultrasonic absorption, excess volumes and mutual solubilities of mixtures of methyl cyanide and water are reported together with the near infra-red absorption spectra of 6 m HOD in deuterium oxide containing methyl cyanide. These properties of methyl cyanide and water mixtures are compared with those of tertiary butyl alcohol and water mixtures and discussed in terms of the effects of added methyl cyanide on the structure of water.

Defects in Rutile. III. Optical and Electrical Properties of Impurities and Charge Carriers

Abstract: Optical absorption spectra of various OH (OD) complexes in rutile have been studied as a function of light polarization, impurity concentration, and temperature. It is shown that the ${\mathrm{H}}^{+}$ (${\mathrm{D}}^{+}$) occupies sites in the basal plane, probably displaced somewhat from \textonehalf{}00, and can associate with various +3 substitutional cations, causing a shift of the OH (OD) stretching vibration to higher frequencies. Harmonic and combination-mode absorption has also been observed. Detailed absorption spectra and their polarization dependence for conduction-band electrons and for electrons in an Fe impurity band are presented, and the strength of the absorptions is related to the carrier concentration. These spectra apparently result from intra- or interband transitions of electrons. In neither case is a simple Drude-type absorption (as in a metal) adequate to account for the spectra. Preliminary data on the Fe impurity band indicate conductivity g0.1 ${\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}1}$ ${\mathrm{cm}}^{\ensuremath{-}1}$ at room temperature for a carrier density of \ensuremath{\sim}7\ifmmode\times\else\texttimes\fi{}${10}^{19}$/${\mathrm{cm}}^{3}$. Qualitative information on diffusion and solubility of various cation impurities is given. These data and results presented in the preceding papers permit a fairly complete, though not yet quantitative, description of the electronic defect structure of rutile. In particular, it is concluded that rutile does not normally exhibit $p$-type conductivity, because of the ease of formation of ${\mathrm{Ti}}^{4+}$ interstitials; and that the donor defect in "reduced" rutile may be either ${\mathrm{Ti}}^{4+}$ or ${\mathrm{H}}^{+}$, depending on reduction temperature and ambient atmosphere, or may be any of a wide variety of metal impurities if these are present.