Showing papers on "Absorption band published in 1979"
TL;DR: In this article, the authors measured the optical absorption spectra of solvated electrons in H/sub 2/O and D/sub O and found that the spectrum at a given A/A/sub max/ shows a shift of +0.05 eV in the low-energy wing, reaching 0.03 eV at the absorption maximum.
Abstract: The optical absorption spectra of solvated electrons in H/sub 2/O and D/sub 2/O have been measured at 274, 298, 340, and 380 K. All the spectra were fitted very well with the Gaussian and Lorentzian shape functions at the low- and high-energy sides of the absorption maximum, respectively, excluding the high-energy tail. The spectrum does not shift uniformly with temperature. The temperature coefficient of absorption decreases rapidly with increasing energy on the low-energy side of the absorption maximum, while it changes only slightly on the high-energy side. When the temperature increases the Lorentzian width remains constant, the Gaussian width varies proportionally to T/sup 1/2/, and the spectrum becomes more symmetrical. On going from H/sub 2/O to D/sub 2/O we found that the spectrum at a given A/A/sub max/ shows a shift of +0.05 eV in the low-energy wing. The shift decreases with increasing energy, reaching 0.03 eV at the absorption maximum. On the high-energy side of the band the shift becomes negative at h..nu.. > 2.2 eV. The shift on the low-energy side seems to be related to the difference of the zero-point energies of the inter- and intramolecular vibrations. The wavelength dependence of the temperature and isotope effects ismore » consistent with the model that different types of excitation occur on the low- and high-energy sides of the absorption band. The temperature and isotopic dependence of the low-energy side are consistent with its width being due to phonon interactions.« less
215 citations
TL;DR: In this article, it was shown that dipole-dipole interactions are responsible for the shift of the CO stretch absorption band to higher frequencies as a function of increasing coverage.
205 citations
TL;DR: In this paper, a tetragonal crystal field splitting of both the 4f1 ground state and 5d1 excited states of YAG:Ce3+ in YAG has been investigated.
Abstract: Absorption and luminescence spectra of YAG:Ce3+ crystals have been measured at various temperatures between 4.2° and 300°K. The high resolution, low temperature spectra show resolved fine structure. Zero‐phonon transitions have been assigned and the phonon replicas correlated with lattice phonon energies. The characteristic absorption band of YAG:Ce3+ near 460 nm decreases in intensity, whereas that near 340 nm increases with increasing temperature. This effect is explained in terms of a tetragonal crystal field splitting of both the 4f1 ground state and 5d1 excited states of Ce3+ in YAG. When allowance is made for changes in the absorption of pump light with temperature the photoluminescence quantum efficiency of Ce3+ in YAG is constant up to 300°K. The significance of these crystal field effects for the use of YAG:Ce as a high temperature lamp phosphor is discussed.
172 citations
TL;DR: In this paper, a band shift rule was proposed to predict the spectral shift between the absorption features due to the complex and the absorption band of uncomplexed iodide atoms in the van der Waals molecule I2Hen.
Abstract: The process of photodissociation of the van der Waals molecules I2He, I2He2, and I2He3 has been studied. Vibronic state distributions of the electronically excited product I2* fragment produced upon photodissociation have been measured by observing the dispersed fluorescence spectra of these fragments. It was found that for each complex I2Hen, the first observed dissociation channel involved the loss of n vibrational quanta from the I2 stretch even though channels involving the loss of fewer quanta were energetically open. The n quantum channel was by far the dominant channel although some weaker n+1 processes were observed. Branching ratios are reported. It was found that the various complexes can be identified by a band shift rule which accurately predicts the spectral shift between the absorption features due to the complex and the absorption band of uncomplexed iodine. This rule says that the spectrum shifts a constant amount for each additional helium atom in the complex. The cross section for collisional vibrational relaxation of I2 by helium in a supersonic expansion was measured as a function of position from the supersonic nozzle. It was shown that the effective vibrational relaxation cross section increases as the translational temperature and relative kinetic energy decreases.
125 citations
TL;DR: In this article, a pulsed-dye-laser optoacoustic spectroscopy technique was used to measure the weak visible absorption band of benzene near 607 nm, due to the sixth harmonic of the C-H stretch.
Abstract: We report a pulsed‐dye‐laser optoacoustic spectroscopy technique for sensitive measurements of weak absorption spectra of liquids. We have used this technique to measure the weak visible absorption band of benzene near 607 nm, due to the sixth harmonic of the C‐H stretch. We obtain a signal‐to‐noise ratio exceeding 102 at the absorption peak. We estimate that with improved data handling, absorption features as small as 10−7 cm−1 should be detectable in liquids. This opens up new possibilities of trace‐constituent detection and pollution monitoring in the liquid phase.
99 citations
TL;DR: In this paper, the spectrum of the complex ions M(bipy) 2+3 (M = Fe, Ru, Os) has been determined, together with the CD of the corresponding optical isomers at low temperature.
96 citations
TL;DR: The reflectance spectrum for integral Mercury is presented from 0.65 to 2.5 μm in this article, and a weak, broad absorption band appears centered at 0.89 μm, probably due to electronic transitions in Fe2+ ions in the soil.
Abstract: The reflectance spectrum for integral Mercury is presented from 0.65 to 2.5 μm. The reflectance continues to increase from the visible spectral region into the infrared, and a weak, broad absorption band appears centered at 0.89 μm. The absorption is probably due to electronic transitions in Fe2+ ions in the soil. The band center position suggests an orthopyroxene as the major mafic mineral affecting the spectrum. The band strength and the soil albedo suggest that the amount of Fe2+ present is similar to that for lunar highland soil.
95 citations
TL;DR: In this paper, the diffuse reflectance spectra of the microcrystalline Cu/ZnO solids provide evidence for interactions between an x-ray amorphous or solute form of copper and the ZnO wurtzite crystals.
Abstract: Diffuse reflectance spectra of the microcrystalline Cu/ZnO solids provide evidence for interactions between an x-ray amorphous or solute form of copper and the ZnO wurtzite crystals. These interactions result in the emergence of a new absorption band at 17,500 cm/sup -1/ and the simultaneous spectral disappearance of the 25,800-cm/sup -1/ fundamental absorption edge of zinc oxide. This behavior is most pronounced when the copper concentration in the zinc oxide phase reaches the saturation value of 17 +- 1%. The copper solution in the zinc oxide is a highly degenerate semiconductor with a strong light absorption intensity in the visible region of the spectrum. A comparison with earlier observations of methanol synthesis activity of the Cu/ZnO catalysts shows that specimens containing a maximum amount of copper dissolved in the zinc oxide are also the best catalysts for methanol synthesis.
95 citations
TL;DR: In this paper, optical absorption spectra were reported for Li, Na, and Ag in various stages of aggregation ranging from atom to microcrystal, and it was shown that the trimers are triangular and the four atom clusters have tetrahedral shape.
Abstract: Optical absorption spectra are reported for Li, Na, and Ag in various stages of aggregation ranging from atom to microcrystal. The samples were prepared by the simultaneous condensation of rare gas and metal vapor onto a liquid helium temperature substrate. The dependence of the strength of the individual absorption lines on metal concentration and on selective light induced diffusion allowed the tentative assignment of spectral features to one, two, three, and four atom clusters. Comparison of the observed transition energies with an empirical, extended Huckel calculation seems to indicate that the trimers are triangular and the four atom clusters have tetrahedral shape. For metal concentrations higher than 10% the sharp molecular lines abruptly disappear and a single broad plasmon absorption, characteristic of microcrystals, appears. The shape of this absorption band can be explained using a continuum theory of dielectric response if microcrystal size, shape, and mutual interaction are properly taken in...
95 citations
TL;DR: In this paper, the complex index of refraction for amorphous SiO2 is derived in the energy range 0.03 − 1.0 eV by Kramers-Kronig analysis of reflectance data.
Abstract: The complex index of refraction N=n−ik for amorphous SiO2 is derived in the energy range 0.03–1.0 eV by Kramers‐Kronig analysis of reflectance data. The results are used to compute the transmission, reflectance, and absorptivity of thin layers of SiO2 on Si substrates in the vicinity of the 0.14‐eV (9 μ) lattice absorption band of SiO2. The dependence of these quantities on the layer thickness and angle of incidence is discussed.
89 citations
TL;DR: Raman frequency shifts are used to estimate differences in bond strain energies between MbIIIX and HbIIIX (X = OH-, F-).
Abstract: Resonance Raman spectra and excitation profiles have been obtained within the 5700-6300-A absorption band of purified sperm whale metmyoglobin hydroxide (MbIIIOH) solutions. A large enhancement occurs for a Raman peak at 490 cm-1 which is shown by isotopic substitution of 18O for 16O to be almost purely an Fe-O stretch. The Fe-O vibration in MbIIIOH occurs 5 cm-1 to lower energy than the corresponding vibration at 495 cm-1 in human methemoglobin hydroxide (HbIIIOH) [Asher, S., Vickery, L., Schuster, T., & Sauer, K. (1977) Biochemistry 16, 5849], reflecting differences in ligand bonding between Mb(III) and Hb(III). A larger frequency difference (10 cm-1) exists between MbIIIF and HbIIIF for the Fe-F stretch. We do not observe separate Fe-O or Fe-F stretches from the alpha and beta chains of either HbIIIOH or HbIIIF. Excitation profile measurements for MbIIOH indicate that the 5700-6300-A absorption band is composed of two separate absorption bands which result from a high- and a low-spin form of MbIIIOH. The spin-state-sensitive Raman band at 1608 cm-1 reflects the high-spin species and has an excitation profile maximum at about 6000 A while the low-spin Raman band occurs at 1644 cm-1 and shows an excitation profile maximum at 5800 A. The Fe-O stretch at 490 cm-1 has an excitation profile maximum at about 6000 A. The differences in frequency and Raman cross section between the Fe-X vibrations in MbIIIX and HbIIIX (X = OH-, F-) can be related to increases in the out-of-plane iron distance for the high-spin species of MbIIIX. The shift in the 1644-cm-1 MbIIIOH low-spin state Raman band indicative of the heme core size to 1636 cm-1 in HbIIIOH indicates a larger heme core size in HbIIIOH. Raman frequency shifts are used to estimate differences in bond strain energies between MbIIIX and HbIIIX (X = OH-, F-). Previous resonance Raman excitation profile data can be interpreted in terms of separate contributions from different spin-state species.
TL;DR: The resonance Raman spectra of riboflavin bound to egg-white proteins were observed for N(3)-H and N( 3)-D forms with spontaneous Raman technique by using the 488.0-nm excitation line of an argon ion laser for elucidating the structure of electronically excited states of isoalloxazine.
Abstract: The resonance Raman spectra of [2-13C]-, [4a-13C]-, [4-13C]-8 [10a-13C]-, [2,4,4a, 10a-13C]-, [5-15N]-, [1,3-15N]-, and [1,3,5-15N]riboflavin bound to egg-white proteins were observed for N(3)-H and N(3)-D forms with spontaneous Raman technique by using the 488.0-nm excitation line of an argon ion laser. The fluorescence of riboflavin was quenched by forming a complex with egg-white riboflavin binding protein. The in-plane displacements of the C(2), C(4a), N(1), N(3), and N(5) atoms during each Raman active vibration were calculated from the observed isotopic frequency shifts. The 1252-cm-1 mode of the N(3)-H form was found to involve large vibrational displacements of the C(2) and N(3) atoms and to be strongly coupled with the N(3)-H bending mode. This line can be used as an indicator for state of N(3)-H...protein interaction. The 1584-cm-1 mode, which is known to be resonance-enhanced upon excitation near the 370-nm absorption band, was accompanied by the displacement of the N(5) atom in particular. The 1355-cm-1 mode was most strongly resonance-enhanced by the 450-nm absorption band and involved the displacements of all carbon atoms of ring III. Both lines can be used as structure probes for elucidating the structure of electronically excited states of isoalloxazine.
TL;DR: The geometry of the dimeric primary donor seems to be affected by the presence of a negative charge in the reaction center.
TL;DR: In this article, the authors used the theory of impurity centers in the quantitative analysis of structured optical spectra through the use of formulas relating the absorption band shape to the shape of the fluorescence band.
Abstract: Recent developments in the theory of impurity centers are reviewed. Particular attention is devoted to the way this theory can be exploited in the quantitative analysis of structured optical spectra through the use of formulas relating the absorption band shape to the shape of the fluorescence band. Analysis of departures from mirror-image relation between these two spectra can be used to deduce the parameters of the electron-phonon coupling from the shape of the structured bands. Topics discussed include zerophonon lines, the dependence of their shape and position on temperature, departures from mirror-image relation for both phonon wings and the vibronic absorption and fluorescence spectra, the energy gap between the absorption and fluorescence spectra of certain molecules, and the nature of excimer emission in solids.
TL;DR: In this paper, the results of an investigation of two-photon absorption in liquid benzene using the opto-acoustic (OA) technique have been reported, showing that far superior spectra can be obtained by the simple and sensitive twophoton OA spectroscopy (TPOAS) technique.
Abstract: THE recently developed high-sensitivity opto–acoustic (OA) absorption measurement technique1 has proved ideal for the measurement of a variety of weak absorption phenomena in liquids2–4 We report here the results of an investigation of two-photon absorption in liquid benzene using the OA technique Weak two-photon spectra (cross-section ≲10−51 cm4 molecule−1 photon−1 s) in nonfluorescing liquids have been difficult to measure The only previous published study for such a measurement used thermal blooming5, which is difficult to interpret theoretically and apparently produces a poor signal-to-noise ratio We demonstrate here that far superior spectra can be obtained by the simple and sensitive two-photon OA spectroscopy (TPOAS) technique Polarisation dependence, vibrational intervals and electronic origin are obtained, and two-photon absorption cross-sections are derived for the first time in this study for the case of a weak two-photon absorption band in liquid benzene Note that Bonch-Bruevich et al6 have recently attempted similar two-photon OA measurements, but they can only measure strong absorption (cross-section ≳10−48 cm4 molecule−1 s) with a poor signal-to-noise ratio
TL;DR: It is shown that nonlinear optical processes such as multiphoton absorption and stimulated Raman scattering in liquids should be readily observable with the optoacoustic method.
Abstract: We use the recently developed technique of pulsed dye-laser optoacoustic spectroscopy of liquids to study the weak 607-nm absorption band of benzene dissolved in various concentrations in CCl(4). The technique involves the use of submersed piezoelectric transducer and gated detection of the transient acoustic signal. With increasing dilution, the peak of the 607-nm band is observed to be more blue-shifted, and the linewidth and asymmetry of the band decrease. We verify that the present technique can detect absorption coefficients of 10(-6) cm(-1) and absorbed energy of 10(-9) J. With these high sensitivities, we show that nonlinear optical processes such as multiphoton absorption and stimulated Raman scattering in liquids should be readily observable with our optoacoustic method.
TL;DR: In this article, a three-body reaction with a rate constant of (1.0±0.3) × 10−32 cm 6 sec−1 was studied by monitoring the time dependence of the 987.6 nm absorption band due to Ar*2 under various conditions.
Abstract: Argon excited diatomic molecules Ar*2(3J+u)were produced by irradiating argon gas with short electron beam pulses. The kinetic behavior was studied by monitoring the time dependence of the 987.6 nm absorption band due to Ar*2 under various conditions.The method is largely different from the vacuum UV emission spectroscopy used previously in such kinetic studies. Ar*2 was found to be produced by a three‐body reaction with a rate constant of (1.0±0.3) ×10−32 cm 6 sec−1. Then, the rate constants and cross sections of energy transfer were determined for 12 fundamental acceptor molecules. The theoretical formula proposed previously for Penning ionization was applied to energy transfer between Ar*2 cross sections given by the formula have the values comparable to the observed ones.
TL;DR: Light-harvesting bacteriochlorophyll-protein complexes from Rhodopseudomonas sphaeroides 2.1 and R-26 mutant are solubilized in sodium dodecyl sulfate and imbedded in polyvinyl alcohol and the linear dichroism of visible and near infrared absorption is analyzed.
TL;DR: The photoabsorption of atomic Fe, Co, Ni and Cu has been determined in the energy range from 45 to 90 eV as discussed by the authors, where the dominant absorption band is conserved in the spectra of the metals whereas the rich atomic fine structure at the 3p threshold and approximately 10 eV above is washed out.
Abstract: The photoabsorption of atomic Fe, Co, Ni and Cu has been determined in the energy range from 45 to 90 eV. For Co, Fe and Ni there is a strong asymmetric resonance at the 3p threshold which is attributed to 3p63dn to 3p53dn+1 transitions. These transitions are split by the interaction of the 3p hole with the partly filled 3d shell and the 3p spin-orbit interaction and considerably modified by the interaction with the 3p63dn to 3p63dn-1 epsilon f transitions. The two channels are strongly coupled bia the 'super Coster-Kronig' decay 3p53dn+1 to 3p63dn-1 epsilon f. The dominant absorption band is conserved in the spectra of the metals whereas the rich atomic fine structure at the 3p threshold and approximately 10 eV above is washed out. The 3d shell is filled in Cu and therefore the strong 3p-3d resonance is missing in the spectra of atomic and metallic Cu.
TL;DR: In this paper, the interaction of NO + CO with 5% Rh/Al 2 O 3 was investigated by infrared spectroscopic measurements in the temperature range 25-400°C.
TL;DR: In this article, an intense 6 ns laser pump pulse tuned to the absorption maximum of the longest wavelength, ground state absorption band was used to generate excited states of laser dyes.
Abstract: Excited states of laser dyes were generated in solution by an intense 6 ns laser pump pulse tuned to the absorption maximum of the longest wavelength, ground state absorption band. They were interrogated by a shorter, simultaneous, monochromatic pulse of smaller diameter, concentric and collinear with the pump, having a crossed polarization. Plots of transmission curves against intensity for the pump beams approached residual absorptions at the highest intensities. Gain or attenuation of the probe was measured throughout the region of the long wavelength absorption bands, at the 578.2 nm copper vapor laser wavelength, and for rhodamine 6G across the lasing band. Gains were determined at different probe intensities, and were extrapolated to small-signal values. The dyes have fluorescences at the ground state absorption maxima, hence pumping at these wavelengths cannot achieve 100 percent S 1 population. Auxiliary saturation transmissions were determined beyond the fluorescence bands and the first experiments were corrected to give a measure of \sigma_{e} - \sigma^{\ast} , the difference between the stimulated emission cross section and the excited state absorption cross section. Assumptions in the experiment and improvements in experimental technique are discussed.
TL;DR: A well-resolved absorption band system, observed between 3400 and 3100 A after a flash discharge through methylsilane, is ascribed to the free H 2 CSi radical as discussed by the authors.
TL;DR: Karickhoff et al. as mentioned in this paper investigated the role of Fe(III) in the specific UV absorption of smectites and found that reduction with hydrazine fumes resulted in the disappearance of the peak and reoxidation with H202 caused its reappearance with even stronger intensity than originally.
Abstract: UV-visible light absorption spectra of dilute suspensions of standard and com- mercial montmorillonites (bentonites) and of nontronite, hectorite and pyrophyllite, were stu- died. All montmorillonites exhibit either an absorption band or a shoulder at a wavelength of 245 nm. The absorption peak for nontronite is shifted to 260 nm and absorption intensity is very high. Hectorite exhibits a very slight shoulder whereas pyrophyllite shows almost none. Absorption intensity in the UV range was found to be in direct correlation to structural octahedral Fe(III) contents. Direct evidence for the role of Fe(III) in the specific UV absorption of smectites was obtained by the fact that reduction with hydrazine fumes resulted in the disappearance of the peak and reoxidation with H202 caused its reappearance with even stronger intensity than originally. M6ssbauer spectra showed that the Fe(III) disappeared almost completely in the reduced clay. Light absorption characteristics of clay minerals in the UV and visible range have been studied by several investigators (Faye, 1968; Banin & Lahav, 1968a; Karickhoff & Bailey, 1973). Visible absorption spectroscopy has been reported as a useful technique for the estimation of particle size of clays in suspension (Kahn, 1959; Banin & Lahav, 1968a, b). Banin & Lahav (1968b) noted that montmorillonite (Wyoming Bentonite) shows a light absorption band in the UV range, at about 245 nm. They proposed a semiquantitative method for the estimation of the specific light absorption intensity by subtracting the estimated scattered light from the optical density at the absorption band. They further postulated that the absorption band in montmorillonite is caused by compounds which are affecting the tactoid size of the mineral while dispersed in water. This suggestion was based on the fact that a negative correlation was found between the intensity of light absorption and tactoid size. Faye (1968) studied the electronic spectra of several clay minerals (not including montmorillonite) and reported an intense absorption band for chlorite at about 255 nm. Based on energetic considerations Faye concluded that this band resulted from Fe+2---~A1.3 charge-transfer. Karickhoff & Bailey (1973) studied the UV and visible absorption spectra of a number of clay minerals. Based on the comparison of their spectra with those of simple oxo-inorganic compounds doped with iron(Ill) as reported by Lehmann (1970), they concluded that UV absorption bands of montmoril- lonite and nontronite are due to oxo-octahedral iron(Ill) electron charge transfer. At present, data in the literature are limited to certain montmorillonites from the U.S.A. and the evidence for the contribution of iron to the UV absorption of clay minerals cited above, is indirect. The objectives of the following study were to examine smectites from some other sources and to present direct evidence and identification of the light- absorbing species.
TL;DR: In this article, a fundamental many-particle theory of temperature-dependent spectral moments is developed for the enhanced optical absorption bands attributed to solvated electrons in various polar solvents.
Abstract: A fundamental many-particle theory of temperature-dependent spectral moments is developed for the enhanced optical absorption bands attributed to solvated electrons in various polar solvents. Several new results are obtained (expressed in atomic units): (1)n0ƒ= 1, where n0 is a mean index of refraction of the solvent and ƒ is the empirical oscillator strength of the band; (2)〈∣Δre∣2〉=(1/ω)av, where 〈∣Δre∣2〉 is an equilibrium-averaged dispersion-in-position of the solvated electron and (1/ω)av is the mean reciprocal absorption frequency of the band; (3)µe–¾ωav, where µe is the standard chemical potential of the solvated electron and ωav is the mean absorption frequency of the band; (4)ωth⩽¾ωav, where ωth is the (vertical) photoejection threshold frequency of the solvated electron.For solvated-electron spectra in ammonia, water and a number of other solvents, no more than about 25 % of the pertinent absorption band can be ascribed to bound–bound transitions involving excited states with energies less than that of the photoejection threshold of the solvated electron.
TL;DR: In this article, double resonance measurements of the SF6 ν3 mode spectral region for excitation levels of up to 1.2 J/cm2 are reported, and the induced spectrum of the ν 3 mode shows a pronounced red shift.
Abstract: Infrared–infrared double resonance measurements of the SF6 ν3 mode spectral region for excitation levels of up to 1.2 J/cm2 are reported. Immediately following the pump laser excitation, the induced absorption spectrum of the ν3 mode shows a pronounced red shift. The spectrum then shifts to shorter wavelengths on a time scale of several microseconds, showing a cooling of the ν3 mode. At an excitation level of 3 photons/molecule the measured spectra approach the thermal spectrum expected for complete vibrational energy thermalization among all of the vibrational degrees of freedom on a time scale of 3±2 μsec. At higher excitation levels (∼10 photons/molecule) the induced spectrum still shifts on a comparable time scale but is broader than a thermal spectrum. At the lower fluence levels (∼3 photons/molecule), a ν3 mode temperature can be assigned to the spectra. The time evolution of this temperature exhibits only a weak pressure dependence. A much broader induced absorption band, approximately a factor of ...
TL;DR: In this paper, it was shown that the IR overtone region is more suitable for the study of liquid water or aqueous solutions than the IR fundamental region, due to the higher intensity of the absorption bands of the free OH vibration compared to the H-bonded OH groups.
TL;DR: In this paper, the Kramers-Kronig transformation was used to derive the absorption spectra of a K-TCNQ single crystal at 27,295 and 413 K.
TL;DR: In this paper, it was shown that the 1.979 and 2.367 eV centres are the same defect in two different orientations with respect to the diamond lattice.
Abstract: A vibronic centre with a zero phonon line at 2.367 eV is produced in type $\text{I}b$ diamond by electron irradiation. The absorption system associated with the centre is strongly photochromic, and at low temperature (less than 200 K) may be bleached to less than 10% of its original strength; as the 2.367 eV system is bleached an absorption band with a zero phonon line at 1.979 eV is produced. The process may be reversed by warming the sample to room temperature. The temperature dependence of the thermal recovery process has been analysed to obtain the associated activation energy, and the temperature dependences of the intensities of the 1.979 and 2.367 eV zero phonon lines have been investigated in the temperature range 5-100 K. Analysis of the data shows that both zero phonon lines are due to transitions from split ground states, and the splittings and relative degeneracies of the levels in the two ground states have been determined. No photoconductivity associated with absorption at the 2.367 eV centre has been detected, suggesting that the bleaching phenomena are not due to a change of charge state of the centre or a charge transfer process. It is therefore proposed that the 1.979 and 2.367 eV centres are the same defect in two different orientations with respect to the diamond lattice. The activation energy associated with the thermal recovery of the 2.367 eV system after bleaching may then be identified with the reorientation energy of 1.979 eV centres. The 2.367 eV centre is unstable on thermal annealing, being virtually destroyed at 200 degrees C. A probable model for the centre is a substitutional nitrogen-interstitial complex, involving at least two interstitials.
TL;DR: In this paper, it was shown that the 5.3 eV band, created by atomic displacement collisions resulting from energetic particle bombardment, is associated with an F-type center.
Abstract: Heating spinel (MgAl2O4) single crystals in aluminum or magnesium metal vapor at temperatures in excess of 1800 °C results in the introduction of an optical absorption band at 5.3 eV. The same band can be produced by heating in a strongly reducing atmosphere with no metal vapor at 2100 °C. These results strongly support the suggestion of Bunch that the 5.3‐eV band, created by atomic displacement collisions resulting from energetic particle bombardment, is associated with an F‐type center. Isothermal annealing of the 5.3‐eV band in MgAl2O4 and the 5.0‐eV band in MgO introduced by thermochemical coloration suggests that the activation energy for oxide‐ion vacancy motion is, respectively, 1.8 and 3.4 eV.
TL;DR: In this paper, the radial distribution function (RDF) curves of two glasses, Na2O·V2O5·2TeO2 and Cs2OµV2õ5µ2TeõO2, were obtained by an X-ray diffraction study.
Abstract: The crystal line phases Me2O·V2O5·2TeO2 (Me=Li, Na, K, Cs, Ag) and their glasses are studied with the aid of infra-red spectroscopy. The radial distribution function (RDF) curves of two glasses, Na2O·V2O5·2TeO2 and Cs2O·V2O5·2TeO2, are obtained by an X-ray diffraction study. An attempt is made to identify the main bands in the infra-red spectra of the crystalline compounds and the glasses. The absorption bands in the 970 to 880 cm−1 range are assigned to the stretching modes of the VO2 isolated groups. A trend is observed towards a shift of the high-frequency band by the replacement of an alkaline ion with another in the order Ag+, Cu+, Li+, Na+, K+, Rb+, Cs+, which is explained by their different polarizing ability. With the aid of X-ray diffraction studies it is shown that the basic structure units in the glasses studied are the VO4 and TeO4 groups.