Additional Absorption Band Research Articles

The 0.9 eV Absorption Band of Polyaniline: A Morphologically Sensitive Electronic Absorption

The optical absorption spectra of polyaniline in the visible and UV spectral regions have been characterized before. The electrically conductive form has a band gap absorption at 3.8 eV and polaron absorptions at 2.9 and 1.5 eV [1,2] . An additional electronic absorption band at 0.9 eV was found to be also related to the existence of polaron. The assignment of this transition has yet to be made. Epstein and co-workers [31 have found a photo-induced absorption band at 0.9 eV by photo-exciting emeraldine base (insulator) with 2.0 eV light. It is not known yet whether these two 0.9 eV transitions belong to the same set of electronic energy levels of polaron, or they belong to two different electronic systems but are coincidentally have the same transition energy.

Defects in the electronic structure of poly (p-phenylene vinylene): Electronic spectra, electrochemical behavior, and molecular orbital calculations

The electronic spectrum of thin films of poly(p-phenylene vinylene) (PPV) in an insulating neutral form exhibits three absorption bands with maxima at 6.12, 5.06, and 3.08 eV. The first two maxima are related to localized molecular states and the broad band at 3.08 eV is described in terms of a vibrationally coupled exciton model. Upon electrochemical doping of PPV, two additional absorption bands appear at 0.80 and 2.10 eV which are associated with a dication whose charge is spread over a few monomer units. Thin films of PPV can be electrochemically converted from the oxidized (conducting) form to the neutral (insulating) form repeatedly in LiAsF6/propylene carbonate solution without evidence of decomposition. The E0 measured using cyclic voltammetry is 3.85 V vs a Li/Li+ reference electrode; however, the observed optically active defects occur in a region of higher potential.

Triplet-triplet absorption spectra of phenanthrene and azaanalogues

Triplet-triplet (T-T) absorption spectra of phenanthrene and several azaanalogues were measured in the spectral range from 25000 to 17000 cm −1 at 83 K. For the first time a vibrational structure of the main band systems in the T-T spectra could be detected. The vibrational modes producing these progressions are associated with the lower T 1 state. The assignment of the vibrational structure to the T 1 state has been confirmed by computation of the T-T spectra with the help of a lineshape function. Furthermore, in the spectra of the azaanalogues an additional absorption band appears which is assigned to a T-T transition from the T 2 state.

The influence of the water content on absorption and dispersion behaviour of calcium metaphosphate glasses

Calcium metaphosphate glasses were prepared with a water content between 0.005 and 0.16 mol 1 −1 . Properties measured vary in a characteristic way in dependence on the water content. An interpretation for the shift of the absorption edge to shorter wavelength with increasing OH-group concentration, which also explains the change of the glass transition and the recrystallization temperature, is proposed. Dispersion calculations for the wavelength dependence of the refractive index refer to an additional absorption band caused by the OH-groups on the short-wavelength side of the absorption determining the UV-edge

Excitonic Structures of Thin Alkali Iodide Crystals

Thin crystals of KI and RbI with 0.1∼10 µm thickness have been grown from the melt inside the narrow gap of a quartz cell, and their absorption and reflection spectra have been investigated near the fundamental absorption edge at 11 K. In both crystals, when the thickness is decreased to ∼0.5 µm, additional absorption bands are found to appear just below the n =1 and n =2 exciton bands. With further decrease in the thickness, they become intense and shift to lower energy. These additional structures are attributed to the pure triplet exciton states induced by the strains in thin crystals. This assignment is discussed in terms of the exciton model in alkalihalides.

Optical properties of iron-doped CuInTe 2

Optical absorption spectra of CuInTe 2, Cu 0.995Fe 0.005InTe 2 and CuIn 1− x Fe x Te 2 single crystals with x=0.01 and 0.1 are measured in the photon energy range hv=0.2–1.1 eV. In CuInTe 2 and CuIn 1− x Fe x Te 2 the spectra are governed by residual absorption effects and intervalence-band transitions without any iron-related absorption bands. Hole effective mass ratios of m lh m hh = 0.098 and m sh m hh = 0.16 and a spin-orbit splitting of 0.63 eV at 300 K are derived from an analysis of the intervalence-band absorption spectra. In Cu 0.995Fe 0.005InTe 2 single crystals the spectra exhibit an additional double-structured absorption band peaking at 0.39 eV which is assumed to be due to iron atoms incorporated on copper sites.

An infrared spectroscopic study of the initial species formed on the polymerisation of alkenes on an anatase. TiO 2, catalyst with surface sulphate

Infrared spectra have been obtained from the polymerisation of the alkenes, ethene, propene, isobutene, 1,3-butadiene and styrene on an anatase, TiO 2, catalyst. A surface-sulphate component appears to be necessary for efficient polymerisation. In the case of ethene, propene and styrene the infrared absorption bands obtained in the very early stages of polymerisation are interpretable in terms of a carbene initial species of type RR'C=Ti ∗. with R=H, R′=CH 3 from ethene; R=R′=CH 3 from propene, and R=CH 3, R′=C 6H 5 from styrene. Additional absorption bands in the region 1620 to 1590 cm −1 that do not grow on polymerisation are Interpreted 1n terms of the presence of π-bonded alkenes on the oxide surface; such species are likely to be Involved in an insertion reaction 1n the CTi bond during the formation of polymer chains. Additional absorptions from the C n alkenes with n>2 in the region 1540 to 1515cm −1 are tentatively interpreted in terms of the presence of surface π-allyl species.

IR and Raman studies of polythiophene prepared by electrochemical polymerization

IR and Raman studies have been carried out for polythiophene prepared by electrochemical polymerization and subsequently treated with aq. NH 4OH solution to neutral film. Four additional strong absorption bands at 1330, 1200, 1100 and 1030 cm −1 appeared upon doping irrespective of the nature of dopants and their intensities increased with increasing dopant concentration. Polydeuterothiophene obtained by the same method gave similar additional strong bands shifting slightly to lower frequencies. These four intense IR bands did not appear in the Raman spectra of doped polythiophene films. Origin of these IR bands can be attributed to ring stretching of the charged polythiophene chain.

Induced optical activity in the complex of poly(L‐arginine) with azo dyes

AbstractThe absorption and CD spectra of the complexes of poly(L‐arginine) (PLA) and azo dyes have been measured in aqueous solution. On complexation, Blue‐shifted additional absorption bands were observed. In the wide pH 4–11 range, induced CD was observed at the visible wavelengths corresponding to the blue‐shifted absorption bands. The induced CD arose from the dimeric dye molecules bound to PLA in the α‐helical structure. When a modified analysis of induced CE is made by the excition chirality method, the origin of the induced CD can be assigned to the dipole coupling. The PLA–dye complexes showed the counterlockwise (negative, S) chirality of the transition dipole moments of dyes.

Macphersonite, a new mineral from Leadhills, Scotland, and Saint-Prix, France— a polymorph of leadhillite and susannite

AbstractMacphersonite is white, resinous to adamantine, hardness (Mohs) 2½−3, density 6.50–6.55 gm/cm3 and possesses a perfect cleavage on {010}. Optically it is negative with 2Vα 35–36°, α = 1.87, β = 2.00 and γ = 2.01, α = b, γ = c, and γ = a, dispersion r > v. Polysynthetic twinning, with either coarse or fine lamellae, is common, as are contact twins. Crystals are orthorhombic, tabular on b with a 10.37, b 23.10 and c 9.25 Å, cell volume 2215.8 Å3 and space group Pcab; Z is 8 formula units. The seven strongest lines in the X-ray powder pattern are 3.274 (50) 052; 3.234 (100) 251; 2.654 (90) 351,203; 2.598 (30) 172, 400; 2.310 (30) 004, 371, 0.10.0; 2.182 (30) 263; and 2.033 (30) 234, 452, 154, 1.10.2. Electronprobe-microanalysis-determined chemistry leads to the empirical formula (Pb4.08, Cu0.10, Cd0.07)Σ4.25S0.90 C2.18O10.55(OH)1.58 which yields the ideal formula Pb4(SO4)(CO3)2(OH)2 and hence macphersonite is a polymorph of leadhillite and susannite. The infrared spectrum shows basic similarities to leadhillite and susannite spectra with additional diagnostic absorption bands. Macphersonite shows an identical thermogravimetric behaviour to that of leadhillite. It is associated, in varying combinations, with leadhillite, susannite, cerussite, caledonite, pyromorphite, scotlandite, galena, and the ‘lead hydroxyapatite’ of Temple (1955). The new mineral mimics leadhillite.

Nitrogen on Triton

The near-infrared spectrum of Triton is characterized by strong absorption bands of methane, probably in the solid state. An additional absorption band at 2.16 μm is tentatively identified as the density-induced (2-0) band of molecular nitrogen in the liquid state. The fundamental overtones of this band system cannot presently be observed because of limitations of the terrestrial atmosphere or spectral signal precision. Using the absorption coefficient for this band derived from laboratory observations and from the literature, it is calculated that Triton must have a layer of nitrogen at least tens of centimeters deep over much of its surface; this quantity is plausible in terms of the cosmic abundance of nitrogen and by comparison with Titan where a massive atmosphere of nitrogen exists. The Triton spectrum has been modeled with liquid nitrogen and solid methane, and it is found that the shape of the continuum in two spectral regions can be properly accounted for by adding a spectral component corresponding to fine-grained water frost. It is speculated that yet another component, a dark, solid, photochemical derivative of methane, may occur as a trace contaminant of the surface materials. If much of the surface of Triton is liquid, the radiometric observations of the satellite must be reinterpreted to derive the radius and surface albedo. If there is liquid nitrogen exposed on the surface, the atmosphere of Triton is probably dominated by nitrogen rather than methane because of the much higher vapor pressure of the former. At the calculated subsolar temperature of Triton, the vapor pressure of nitrogen implies a surface atmospheric pressure in the range 0.13 to 0.30 atm.

Geometrical structure of(Tl+)2luminescent center in alkali halides: Presence ofD2handD4hdimer centers

Absorption, emission, and excitation spectra of the ${({\mathrm{Tl}}^{+})}_{2}$ center in KI, KBr, and KCl have been investigated and compared with the excitation spectrum of the ${({\mathrm{Au}}^{\ensuremath{-}})}_{2}$ center with ${D}_{2h}$ symmetry in KCl. Dichroism produced in the ${\mathrm{Tl}}_{2}^{+}$ absorption band after bleaching with polarized light has also been investigated in $\ensuremath{\gamma}$-ray-irradiated KCl:${\mathrm{Tl}}^{+}$. From these results and from the magnetic-circular-dichroism measurements, it is shown that the ${({\mathrm{Tl}}^{+})}_{2}$ absorption bands observed thus far arise from a ${D}_{2h}$-symmetry ${({\mathrm{Tl}}^{+})}_{2}$ center. An additional absorption band called ${A}^{\ensuremath{'}}$, which has been found at a position close to the peak position of the $A$ band, produces an emission band which is different from the previously observed ${({\mathrm{Tl}}^{+})}_{2}$ emission bands. From a systematic investigation of the separation between the ${A}^{\ensuremath{'}}$ and $A$ bands in various alkali halides, it is shown that the ${A}^{\ensuremath{'}}$ band arises from a ${D}_{4h}$-symmetry ${({\mathrm{Tl}}^{+})}_{2}$ center.

VUV absorption in thin MgO films

Amorphous films of MgO prepared by laser evaporation of bulk crystals show anomalous absorption in the region between 5.2 and 9.2 eV. An additional broad absorption band attributable to absorption by O 2− ions in states of low coordination has been observed at 217.5nm (5.7 eV). Amorphous MgO films show no evidence of absorption due to the bulk O 2− exciton at 7.62 eV but do exhibit such a feature when annealed to 800C in air.

UV/V IS/NIR spectrum of β-carotene incorporated in lipid bilayers. FE-MO calculations and comparison with experiment

Abstract When incorporated in the bilayers of lipid vesicles, β-carotene shows an additional absorption band at 520–540 nm which is not observed in non-polar solvents. A widely distributed opinion attributes the new band to aggregates of the pigment, but conclusive evidence for this suggestion has not been given. Since the spectral properties of carotenoids in biological and artificial membranes are essential for understanding their functions in photosynthesis, an attempt is undertaken in this paper to obtain theoretical expressions for the parameters of the π-electron transitions using the FE-MO model of the long conjugated chromophore axis of β-carotene. The calculated values of the characteristic wavelengths and oscillator strengths are in good agreement with experimental data. As a band at 535 nm presents in the theoretical spectrum, it is suggested another mechanism of the origin of the long-wavelength band, namely, well oriented β-carotene monomers interacting with the neighbouring lipid molecules in the bilayer.

Ultraviolet Absorption of Tl+ Ion in K2OKBrB2O3 and Na2ONaBrB2O3 Glasses

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Absorption, fluorescence, and excitation spectra of thallium‐activated rubidium bromide

AbstractAbsorption, excitation, and fluorescence spectra of polycrystalline RbBr: Tl phosphors are presented at various thallium concentrations. For very low thallium content two absorption bands are obtained peaking at 224 and 260 nm. Additional absorption bands appear around 230, 244 267, and 278 nm with rise of thallium content. An asymmetric fluorescence band in the ultraviolet region is obtained at low thallium concentration which can be resolved into two Gaussian emission bands peaking at 317 and 365 nm. Two additional visible fluorescence bands appear at 440 and 535 nm with rise of thallium content. The excitation spectra for the ultraviolet and visible emission bands are found to be different. Accordingly the ultraviolet emission band is attributed to the characteristic A‐emission in Tl+ monomer entering substitutionally and the visible bands are attributed to dimer centers having D4h site symmetry.

Investigation of the metastable state of Na 2[Fe(CN) 5NO] · 2H 2O by optical spectroscopy. II The electronic spectra of the ground and metastable states

The absorption spectra of Na 2[Fe(CN) 5NO] · 2H 2O were measured in the visible region in the range of 3400–7000 Å. In the metastable state, an additional absorption band in the long wavelength range is observed and the transition 2b 2 (d xy)→ 7e(π ∗ −NO) becomes weaker in the excited state indicating a population of the π ∗(NO)-orbital. The laser excited emission spectrum shows a broad luminescence beginning at the excitation line λ = 5145 A ̊ ( 19,436 cm -1 ) with a maximum at about 6250 Å (16,000 cm -1). A strong sharp luminescence at about 7836 Å is registered and may be assigned to a transition 3 b 1( d x 2− y 2 ) or 5 a 1( d z 2 ) to the antibonding π ∗(NO)- orbital. Further the broad luminescence is superimposed by a series of sharp spikes. These sharp spikes can also be observed for several days, when the laser is switched off, and are depending on the crystal orientation.

Effect of High Doses of Gamma Rays on Corn Grains. Part II. Influence on Some Physical and Chemical Properties of Starch and Its Fractions

AbstractSolubility, swelling power, viscosity, alkali number and ferricyanide number were estimated in the starch isolated from both irradiated air‐dried and moist corn grains. An increase in solubility, alkali number and ferricyanide number and decrease in relative viscosity were found in starch isolated from irradiated air‐dried as well as moist corn grains as the dose level was raised. The swelling power increased up to 2 megarad, then decreased rapidly. Infrared analysis revealed an additional absorption band which arises from a new methylene group at 5 megarad. An increase in amylose percentage concomitant with a decrease in amylopectin percentage was found as the radiation dose was increased up to 2 megarad. Above 2 megarad, the opposite was found. The chain length of amylose and amylopectin showed a progressive decrease as the irradiation dosage was raised.

Photoreactivating enzyme from Streptomyces griseus--II. Evidence for the presence of an intrinsic chromophore.

Abstract—Evidence is presented that DNA photoreactivating enzyme from Streptomyces griseus consists of a high molecular protein part and a low molecular chromophore which is released by denaturation. The free chromophore is highly fluorescent and has an absorption maximum at 420 nm. In native photoreactivating enzyme the chromophore fluorescence is almost completely quenched and there is an additional absorption band at 445 nm. Native photoreactivating enzyme spontaneously looses its chromophore following first order kinetics as measured by the increase of fluorescence intensity. A good correlation was found between the increase of fluorescence intensity and the decrease of biological activity, stressing the importance of the chromophore‐protein bond. The presence of DNA greatly retards the spontaneous release of chromophore, and with UV‐irradiated DNA the photoreactivating enzyme is almost completely stable. In five different chromatographic systems, cochromatography of biological activity and enzyme‐bound chromophore was found, thus ruling out the possibility that the observed chromophore belongs to a contamination in the enzyme preparation. Photoreactivating enzyme binds very strongly to Blue‐Sepharose indicating the presence of a positive charge in the polynucleotide binding site.

Liquid Crystal Formation in Binary Systems. II. Induction of Nematic and Smectic Phases by Electron Donor-Acceptor Interaction between the p-Dimethylamino and p-Nitro Derivatives of N-Benzylideneaniline

Abstract The formation of solid molecular complexes and the induction of nematic and smectic phases have been demonstrated with a number of binary mixtures of potentially-mesomorphic electron donors and acceptors of the type N-(p-X-benzylidene)-p-Y-aniline. One of the components contains a dimethylamino group as X or Y, and the other a nitro group as X or Y. The remaining substituents are methoxyl, ethoxyl, or propoxyl groups. The maximum temperature of the nematic phase induced in these electron donor-acceptor systems is higher by 23 to 45 °C than the straight line joining the latent transition temperatures of the two components. The tendency to form a solid complex and that to induce a nematic phase are both shown to a large extent by the propoxy derivatives, to a lesser extent by the methoxy derivatives, and least by the ethoxy derivatives. All the solid molecular complexes are reddish brown and exhibit an additional electronic absorption band located at about 500 nm. The mesophases are similarly colored. The enhanced thermal stability of the nematic and smectic phases in these binary mixtures is ascribed to the complex formation by an electron donor-acceptor interaction.