Observed Reflectance Spectra Research Articles

A Study onZ3-Exciton's Damping in CuCl1-xBrxSolid Solutions

An ω-dependent damping factor of Z 3 -exciton in CuCl 1- x Br x ( x ≥0.012) has been evaluated experimentally, using two-photon resonant Raman scattering (TRRS) based on two-photon excitation of excitonic molecules and linear reflection. A remarkable difference between the shape of the observed reflection spectrum and the corresponding spectrum calculated from the polariton dispersion curve, which was determined experimentally by TRRS for the same sample, has been found in the L-T gap region of Z 3 -exciton of the sample of x =1.2×10 -2 . The difference has been analyzed as the ω-dependence of the damping factor of the exciton level. Its x -dependence has also been studied.

An evaluation of the problems of chlorophyll retrieval from ocean colour, for case 2 waters

A reflectance model is presented that takes into account the spectral signatures of phytoplankton, dissolved organic matter and non-chlorophyllous particles. The model is validated by comparison with observed reflectance spectra. It is then used to simulate a data bank of reflectance spectra for a wide range of combinations of the three optically active substances in various concentrations. The in vivo chlorophyll-a fluorescence is masked. The simulated data are subjected to eigenvector and multiple regression analyses. It appears that the spectral signatures are sufficiently orthogonal to permit retrieval of the concentrations of individual components from the reflectance spectra. However, due to the non-linearity of the system, site-specific algorithms tailored to suit local conditions are likely to yield better results than a single universal algorithm for case 2 waters. Results indicate that the use of 400 nm in addition to the CZCS channels greatly enhances the capability to separate the phytoplankton signal from that of dissolved yellow organic matter. It appears possible to use 5 key-wavelengths (400, 440, 520, 565 and 640 nm) instead of the complete spectrum, without significant loss of information. The consequence of the variability in the backscattering signal of non-chlorophyllous particles is also examined.

Reflection Spectra of (DBTTF)4·(BF4)2·EtOH Complex

Abstract The polarized reflection spectra of the crystal of (DBTTF)4·(BF4)2·EtOH complex were measured and the optical parameters were determined by the simulation of the observed reflection spectra. The theoretical analysis of the observed spectra shows that the electronic structure of DBTTF cation molecules is typical of the island type configuration. The 4000 and 11500 cm−1 bands polarized parallel to the stacking axis were assigned to the CT2 and CT1 bands, and the parameters U and t of the Hubbard Hamiltonian were estimated to be (U=8950 cm−1 and t=1250 cm−1.

Diffused germanium dichroic mirror for optically pumped far-infrared lasers

A new type of dichroic reflector has been developed for the far-infrared region of the spectrum, based on n-type germanium with a diffused conduction layer. A 111-axis single-crystal plate of 40-Ω cm optical-grade germanium was implanted with 5×1014 As+ ions/cm2 by ion bombardment at 200 keV; the donor impurity ions were subsequently diffused into the substrate at a temperature of 850 °C (held for 20 h). The measured power-reflection spectrum displayed a shallow minimum at ∼70 cm−1, rising steeply below 50 cm−1 to reach 80% reflectivity at 10 cm−1. Computer modeling of the infrared reflectance of a thermally diffused conducting layer in n-type germanium—with the assumption of Conwell–Weisskopf mobility variation for the conduction electrons—gave an excellent fit to the observed reflection spectrum for an integrated column density of 1014 cm−2 and 10-μm half width, the latter being in good agreement with the value √Dt=11 μm calculated for thermal diffusion under the conditions indicated.

Electronic Spectra of (DBTTF)3· SnBr6 Complex

Abstract The polarized reflection spectra of (DBTTF)3·SnBr6 complex have been measured and the absorption spectra have been determined by the simulation of the observed reflection spectra. The 4000 cm−1 band polarized parallel to the stacking axis has been assigned to the charge resonance(CR) band. The theoretical analysis of the electronic structure of (DBTTF)3·SnBr6 complex has been made for the explanation of the energy and absorption intensity of the CR band.

Low-temperature reflection spectrum of K-TCNQ single crystal

Polarized reflection spectra of a K-TCNQ single crystal have been measured at 27,295 and 413 K. The absorption spectra were derived from the observed reflection spectra by Kramers-Kronig transformation. At 27 K, the near-infrared absorption band which is associated with the charged transfer between TCNQ − ions, splits into a strong sharp peak at 8 × 10 3 cm −1 and a weak broad band at 11 × 10 3 cm −1. These bands were interpreted in terms of the strongly correlated extended Hubbard model including the nearest-neighbor Coulomb interaction.

Near infrared reflection spectra of ammonia frost: Interpretation of the upper clouds of Saturn

Models of the uppermost cloud layer on Saturn indicate that the cloud is composed of solid ammonia, with the cloud particles being initially formed at about 150 K, and subsequently transported upward by convection to colder regions of the atmosphere. For the purpose of comparison with Saturn's near-i.r. reflection spectrum, we have obtained laboratory reflection spectra of ammonia frost corresponding to a variety of deposition rates and deposition temperatures. We find that the spectral location of the strong 3 μm absorption band of solid ammonia is highly dependent upon the manner in which the frost layer is formed. For rapid deposition on a 150 K cryosurface, which closely simulates what we believe to be the cloud formation process on Saturn, the band is centered at 3.29 μm. This band location, together with the apparent absence of gaseous ammonia overlying the solid ammonia cloud, is consistent with Saturn's observed reflection spectrum in the vicinity of 3 μm. Comparison of Saturn's reflection spectrum with that of Jupiter, in the vicinity of 1.3 and 1.6 μm, also supports the hypothesis of a Saturnian ammonia ice cloud. Differences in the two observed reflection spectra are interpreted as due to gaseous ammonia absorption bands for Jupiter being replaced by solid ammonia absorption features, at displaced wavelengths, for Saturn. An important conclusion of this study is that, for the purposes of either cloud interpretation or cloud radiation modeling, the polycrystalline phase of solid ammonia, and in turn its spectrum, is highly dependent upon the manner in which the soled is formed.

Reflectance spectra for sodium and potassium doped ammonia frosts: Implications for Io's surface

This paper reports measurements of the reflection spectra of sodium- and potassium-doped ammonia frosts as a function of alkali metal concentration for the wavelength range 0.35-2.5 microns. The purpose of the measurements was to determine whether or not the reflection spectra for such a solid was compatible with the spectra albedo of Io. The data show that, with a sufficiently large alkali metal concentration, the reflection spectra of the doped ammonia frosts do not display the characteristic ammonia features at 2.0 and 2.25 micron. The high reflectance of the more concentrated samples and the character of the observed reflection spectrum make it difficult to rule out sodium-doped ammonia frost as a surface constituent on Io on the basis of existing data.

On the surface composition of Io

The wavelength dependence of the reflectivity of Io indicates the presence of two materials on the surface of this satellite of Jupiter. These materials are sulfur and an unspecified material ( R 1) which shows a wavelength dependence of its reflectivity for 0.3 μm < λ < 1.0 μm similar to the non-H 2O frost spectrum of the rings of Saturn. A 60/40 admixture of these two spectra matches the observed reflection spectrum of Io from 0.3μm–3 μm, if the spectrum of R 1 is featureless for λ > 1 μm. Sulfur will give rise to a posteclipse brightening. The variation with wavelength of the temperature dependence of the reflectivity of sulfur will allow an observational confirmation of the presence of sulfur on Io. The material R 1 should show a large geometrical albedo. The translucency of sulfur is consistent with the polarization-phase curve to Io. The material R 1 is also required to be translucent. The thermal conductivity of a cooled sulfur powder under vacuum was measured and found to agree with the value determined for the upper layer of Io from observations at 10 μm. It is shown that this agreement is not necessarily meaningful.

Theory of Molecular Polaritons. Application to the Reflection Spectra of Anthracene, 1,5-Bis(dimethylamino)pentamethinium Perchlorate, and Some Other Cationic Dye Crystals

The reflection spectra of anthracene in the 3800 Å region and 1,5-bis(dimethylamino)pentamethinium perchlorate (BDP) in the 4090 Å region are calculated using molecular polariton theory. In the crystal the anthracene transition, oscillator strength f = 0.1, involves weak to intermediate vibronic coupling of molecular exciton states, and the model calculations easily reproduce the main features of the observed reflection spectrum. In contrast, the intense transition (f = 3.31) of the dye BDP involves strong vibronic coupling of molecular excitons, and polariton theory with phenomenological damping constants does not adequately reproduce the “vibrational” structure observed in the reflection spectra. Theory and experiment are reconciled by considering the coupling among and distribution of two-exciton states in which vibronic and vibrational excitations occupy different lattice sites.

Infra-red absorption spectrum of the cuticular surface of drone honey bee wings as revealed by attenuated total reflectance

The infra-red absorption reflected through the shallow surface of wings of drone Apis mellifera did not show the ester groups expected of waxes. The functional groups that would accompany more than 5 per cent of other lipids were also absent. The observed reflection spectrum resembled that of pleated-sheet polyamides. This suggests that the surface of drone wings is comprised of a protein similar to silk, wool, hair, or human skin.