Showing papers on "Absorption band published in 1972"
TL;DR: In this article, the polarization spectra of indole derivatives have been measured in order to confirm the presence of two types of electronic transitions, 1Lb and 1La, in the long-wavelength absorption region, and to determine the direction of their transition moments.
Abstract: The polarized absorption spectra of crystals of indole derivatives have been measured in order to confirm the presence of two types of electronic transitions, 1Lb and 1La, in the long-wavelength absorption region, and in order to determine the direction of their transition moments. The polarization spectra show that the 1A–1Lb electronic transition forms a sharp absroption band with vibrational structures lying below a broader absorption band of the 1A—1La transition. The transition memont direction of the 1Lb makes an angle of 54° to the long axis of the molecule, while that of the 1La lies at an angle of −38° to the same axis. These results were compared with the results of theoretical calculations of the P–P–P SCF MO–CI method.
148 citations
TL;DR: The electronic structure of nitromethane and nitrobenzene has been studied by high-resolution HeI photoelectron spectroscopy and quantum chemical calculations of the INDO type as discussed by the authors.
Abstract: The electronic structure of nitromethane and nitrobenzene has been studied by high‐resolution HeI photoelectron spectroscopy and quantum chemical calculations of the INDO type. The spectra of CH3NO2 and CD3NO2 exhibit six ionization bands below 21 eV. The transitions to the ground and first excited ionic states have extensive vibrational structure which has been identified as the symmetric NO2 bending mode. The spectra of C6H5NO2 and C6D5NO2 contain at least 10 ionization bands below 21 eV with resolved vibrational structure only in the transition to the ground ionic state. The most loosely bound MO of nitromethane has been identified as the 5a1 NO2–σ bonding orbital, and that of nitrobenzene as the b1 ring‐π orbital. The nonbonding a2 π orbital has been assigned to the second and fourth ionization bands in these respective molecules. Using the MO ordering found here, the 198 mμ absorption band of nitromethane is assigned to the π*(2b1)← σ(5a1) transition and the long wavelength bands of nitrobenzene are ...
95 citations
TL;DR: In this article, the authors measured the magnetic circular dichroism of ferrocytochrome c from 350 to 1000 nm and the MCD of ferricytochromec from 350-750 nm.
Abstract: We have measured the magnetic circular dichroism of ferrocytochrome c from 350 to 1000 nm and the MCD of ferricytochrome c from 350 to 750 nm. We present expressions for the shapes of MCD and absorption spectra in the presence of a magnetic field of randomly oriented molecules for the general case in which the absorption band is split in zero field, and the two components of the split band have different intensities. After correcting for the effects of unresolved zero‐field splitting, we find that the ``angular momentum'' of the Q00 band of Fe(II) cyt c is 7.9 μB. We show that the 23‐fold decrease in the MCD of the Q00 band upon oxidation of Fe(II) to Fe(III) is due to about a fivefold increased bandwidth while the oscillator strength and angular momentum remain essentially unchanged. The increase in bandwidth may reflect greater mixing of the porphyrin orbitals with the d levels of the iron ion in the oxidized state. The MCD of Fe(II) cyt c in the near infrared (600–1000 nm) can be decomposed using essen...
76 citations
TL;DR: In this article, the SCF π-electron theory with bond length optimization was used to calculate the effects of solvent polarity on the structure and spectroscopic properties of a simple merocyanine dye.
Abstract: The SCF π-electron theory with bond length optimization, described in part 1, has been used to calculate the effects of solvent polarity on the structure and spectroscopic properties of a simple merocyanine dye. The calculations predict a minimum in energy and oscillator strength of the first absorption band over the range of solvent parameters used, but these extrema should not occur at the same solvent compositions. The measured u.-v. spectra can be interpreted from these results, and the n.m.r. chemical shifts, which change with solvent, can be correlated with calculated net atom charges.
72 citations
TL;DR: In this article, the authors examined the errors in retrieving the number density distribution from planetary occultation data of very low signal intensity and provided a theoretical analysis of the errors related to the intensity of the source, the number of data points per scan, and the degree of data smoothing required before inversion.
71 citations
TL;DR: In this paper, optical absorption and ESR measurements were carried out on et− produced in ethanol at 4°K and the same et− yield for γ radiolysis at 4 and 77°K indicates that electrons are stabilized in pre-existing traps at 4 °K where molecular dipoles remain unrelaxed.
Abstract: Optical absorption and ESR measurements were carried out on et− produced in ethanol at 4°K. The same et− yield for γ radiolysis at 4 and 77°K indicates that electrons are stabilized in pre‐existing traps at 4°K where molecular dipoles remain unrelaxed. et− prior to solvation can be classified into two groups. One with λmax = 1500 nm, W1/2= 4 × 103 cm−1 and Δ Hpp = 5.5 ± 0.5 G is easily photobleached by the infrared light. The other with broad absorption band in the visible and Δ Hpp = 13.5 ± 1.5 G is not photobleached by the infrared light. The successive shift of the absorption spectrum to the higher energy side on warming is interpreted by the molecular reorientation mechanism. et− decay is observed during the solvation process, depending on time required for the solvation. The blue shift of the absorption spectrum on reducing the temperature is attributed to contraction of electron traps.
55 citations
TL;DR: In this paper, the vibrational frequency of carbon monoxide chemisorbed on an atomically clean polycrystalline tungsten ribbon has been studied using reflectance-infrared spectroscopy and ultrahigh vacuum techniques.
52 citations
TL;DR: In this article, the infrared intensities of metal-carbonyl stretching vibrations were investigated using the idealized local symmetry of the terminal carbonyl groups, and it was shown that the total integrated intensities for a set of symmetry-related dipole derivatives were independent of the angle between any two of them and the threefold axis.
Abstract: Publisher Summary This chapter discusses the infrared intensities of metal–carbonyl stretching vibrations. The number of infrared–active carbonyl stretching vibrations of a complex is determined by the idealized local symmetry of the terminal carbonyl groups. When one bond is stretched, no moments are produced in other bonds. In practice, the area beneath a band is measured to finite limits on either side of the band. In carbon monoxide, s–p mixed orbitals from both the carbon and oxygen atoms combine to form the carbonyl group σ–bonding orbital, leaving an outward-pointing s–p mixed orbital on oxygen and another on carbon. Calculations using Slater atomic orbitals indicate that relatively little change in σ-electron density occurs during a small vibration of carbon monoxide but that there are quite large changes of the π-electron density. The position, shape, and intensity of an infrared-active absorption band are solvent sensitive. In a recent report of the relative intensities of carbonyl stretching vibrations of arene tricarbonyl metal derivatives, Brown and Hughes demonstrated that the total integrated intensities for a set of symmetry-related dipole derivatives were independent of the angle between any two of them and the threefold axis. When a molecule contains carbonyl groups that are not symmetry related, reliable bond angles are difficult to calculate, but it seems certain that as vibrational analyses of such molecules are refined, a deeper understanding of the corresponding band intensities will follow.
44 citations
TL;DR: The spectral reflectivity of Mercury has constant positive slope from 0.32 to 1.05 microns, except for the possibility of an absorption feature in the infrared as mentioned in this paper, which indicates that the surface of Mercury is probably covered with lunar-like soil rich in dark glasses of high iron and titanium content.
40 citations
TL;DR: In this article, the shape and intensities of the fundamental bands of liquid methyl cyanide were observed by conventional transmittance method, and the observed absorption indices were corrected for the dielectric-field effect.
Abstract: The shapes and intensities of the fundamental bands of liquid methyl cyanide were observed by conventional transmittance method. Using the refractive indices observed by the ATR method, the observed absorption indices were corrected for the dielectric-field effect. The band shapes were analyzed from the point of view of moment analysis or correlation-function analysis. The results indicate that the shapes of a1-type vibrations are good Lorentzian shapes, while those of the e-type can be explained as superpositions of Lorentzian and Gaussian functions. It is also found that the band-widths of the e-type vibrations were quite different from each other. Taking into account the effect of vibration-rotation interaction on the band-widths, the disagreement could be explained well. From the analyses of the band shapes of ν7 and nu8, the life-time function, ψ(t), was obtained; it represents the decay of the fraction of freely-rotating molecules.
25 citations
TL;DR: The effect of rotational excitation on the electronic relaxation of isolated benzene has been studied by examination of resonance fluorescence generated when narrow-band exciting light is swept through the rotational envelopes of four S 1 ← S 0 absorption bands as mentioned in this paper.
TL;DR: In this paper, the (A 3 Π (1 u ) ← X 1 Σ g + ) absorption band system of Br2 has been fully investigated for the first time at high resolution.
TL;DR: The single crystal polarized absorption spectra of CsCrCl3 and CsMgCl3 have been measured and interpreted in terms of an octahedral ligand field as discussed by the authors.
Abstract: The single crystal polarized absorption spectra of CsCrCl3 and of CsCrCl3 doped into CsMgCl3 have been measured and interpreted in terms of an octahedral ligand field. The intensities of the spin forbidden transitions are found to be very dependent on the chromium ion concentration. In addition, an absorption band which is strongly polarized along the crystallographic c axis is observed at approximately twice the energy of the 10 Dq band. Both of these effects are attributed to magnetic coupling between the chromium ions; the anomalous band is assigned to a ``double excitation'' of the 5E→5T2 transition on coupled pairs of ions. The crystal structure of CsCrCl3 has also been determined. The lattice is hexagonal with P63mc the most probable space group. The lattice constants are a=7.256(3) and c=6.224(3) A, with ρobs=3.24(4) g/cm3 and ρcalc=3.40 g/cm3. Least‐squares refinement, based on F, of counter data has led to a final R index of 0.042. The main structural feature is a linear array of [CrCl6]−4 octahe...
TL;DR: A zero-phonon line has been observed in additively coloured CaF2 at 677-4 nm and additively colored SrF2 with an associated broad absorption band on the high energy side as mentioned in this paper.
Abstract: A zero-phonon line has been observed in additively coloured CaF2 at 677-4 nm and in additively coloured SrF2 at 769.2 nm with an associated broad absorption band on the high energy side. The broad band shows a partly resolved phonon structure related to the single phonon density of states of the crystal. The zero-phonon line and associated broad band are also observed in fluorescence. The excitation spectrum for the fluorescence has been investigated. It is suggested that the centre giving rise to the spectrum is an F3 complex composed of three nearest neighbour F centres aligned along (100). It is shown that the F3 complex may be reoriented by linearly polarized bleaching light.
TL;DR: In this paper, the assignment of several absorption bands associated with these centers was made and the authors showed that the most prominent bands formed by X-irradiation at liquid helium temperature are the F and H bands.
TL;DR: In this paper, the fluorescence and excitation spectra of several condensed aromatic hydrocarbons were measured in the gas phase at low pressures, and the emission from the second excited singlet state (S2 emission) could be observed with some of the compounds studied, in which the first weak absorption band is located close to the second much stronger band.
Abstract: The fluorescence and excitation spectra of several condensed aromatic hydrocarbons were measured in the gas phase at low pressures. The emission from the second excited singlet state (S2 emission) could be observed with some of the compounds studied, in which the first weak absorption band is located close to the second much stronger band. The relative yield of the S2 emission always increased with the increase in the excitation wave number. It has been shown that the occurrence of the S2 emission can be explained in a qualitative way by the state densities and the radiative rates. In coronene, an emission to be regarded as originating from the third excited singlet state was observed.
TL;DR: In this paper, it was shown that the fluorescence generated by pumping the band at 26 649 cm−1 (vacuum) is consistent with its assignment as the 1B1-1A1 electronic origin, but the structure of fluorescence after pumping a neighbouring absorption band suggests some modification of earlier proposals concerning excited state Fermi resonances in pyridazine.
TL;DR: In this article, the polarized absorption spectrum of 2,5-diketopiperazine was measured in the wavelength region from 250 to 160 nm by the use of a vacuum ultraviolet microspectrophotometer constructed in their laboratory, and three absorption bands were found.
TL;DR: In this paper, the absorption spectrum of PO was observed for the first time in the flame using the usual type of atomic absorption spectrophotometer and the continuous H2 lamp as the source, when 1M aqueous solution of H3PO4 was aspirated into airacetylene flame.
Abstract: Molecular absorption spectrum of PO was observed for the first time in the flame using the usual type of atomic absorption spectrophotometer and the continuous H2 lamp as the source, when 1M aqueous solution of H3PO4 was aspirated into air-acetylene flame. This absorption spectrum shows γ system of PO near 2300A, 2380A, 2460A and 2500A, but the absorptions near 2595A, and α and β systems, which was reported by emission spectrometry, were not observed. As the absorption band near 2460A gives the largest absorbance of four bands, the line at 2460A can be used for the determination of phosphorus. The absorption spectrum of PO gives the considerably high background, which may be due to the absorptions of P2O5 and other phosphorous compounds. Moreover, the interferences by some cations such as Na, K and Ca were observed, whereas there was no enhancement of absorption by addition of iso-propylalcohol, which was observed in flame emission. Detection limit was 2mg P/ml at 2460A.
TL;DR: In this paper, the important A2Σ → X2Π (0, 0) absorption band of OH has been remeasured from spectra obtained by flash photolysis of H2O2 vapor.
Abstract: The important A2Σ → X2Π (0, 0) absorption band of OH has been remeasured from spectra obtained by flash photolysis of H2O2 vapor. Accurate wavenumber measurements using thorium standards show that the previous rotational line measurements are about 0.1 cm-1 too large. Measurements are also given for the (1, 0) band of OH and the (0, 0) and (1, 0) bands of OD.
TL;DR: In this article, the spectral properties of the systems with phosphinyl-α-hydroxyalkyl group which may close forming a five-membered cycle via H-bond was studied.
TL;DR: In this paper, the group of simple inorganic anions known to exhibit charge-transfer-to-solvent (C.T.S) absorption bands in solution, have also been found to be effective in the quenching of anthracence fluorescence.
Abstract: The group of simple inorganic anions known to exhibit charge-transfer-to-solvent (C.T.T.S.) absorption bands in solution, have also been found to be effective in the quenching of anthracence fluorescence. Correlation of quenching constants with both the redox potential, when known, and with the energy of the C.T.T.S. absorption band maximum, supports a mechanism involving electron transfer. The data is tentatively interpreted in terms of an excited state charge-transfer complex (‘exciplex’) formation, although no emission band due to an exciplex was detected. No detectable change occurred in the absorption band of anthracene on the addition of the quencher.
TL;DR: In this article, the EPR spectra also indicated the formation of free radicals which were not positively identified, but were distinguished by their tensor parameters and thermal stabilities, as well as an absence of ligand nitrogen hyperfine structures.
Abstract: Copper‐doped L‐alanine crystals exhibit an absorption band in the ultraviolet region. EPR observations indicate that as a result of this uv absorption, multiple conversion takes place in the Cu2+ complexes. In addition to the complexes originally formed by the impurity ions, two others were identified during uv irradiation at 77°K. These were distinguished by their tensor parameters and thermal stabilities, as well as an absence of ligand nitrogen hyperfine structures. The EPR spectra also indicated the formation of free radicals which, however, were not positively identified. On increasing the temperature, these underwent an irreversible transformation accompanied by the formation of yet another copper complex showing a quintet ligand hyperfine structure of 1:2:3:2:1 intensity ratio.
TL;DR: The absorption spectrum of Na β-naphtholate shows an increase in optical density at its long wavelength edge as a function of temperature as mentioned in this paper, and the formation of solvated electrons from the 1S excited state is dependent upon the excitation wavelength.
Abstract: The absorption spectrum of Na β‐naphtholate shows an increase in optical density at its long wavelength edge as a function of temperature. However, fluorescence yield shows a red‐edge effect: it decreases with temperature when excited anywhere in the last absorption band except at its long wavelength edge, where no dependence upon temperature is observed. When β‐naphtholate is confined in a transparent ethylene‐glycol water glass at low temperatures, the fluorescence peak is shifted towards the blue by ∼2000 cm−1. The formation of solvated electrons from the 1S excited state of β‐naphtholate was also found to be dependent upon the excitation wavelength, no electrons being formed at λexc>365 nm. The various observations are interpreted in terms of a mechanism by which electrons are dissociated from the excited singlet state prior to solvent relaxation in competition with internal conversion to the fluorescent, solvent relaxed level.
TL;DR: In this paper, it is suggested that a broad absorption band which occurs in additively coloured CaF2 at 521 nm and in additiveially coloured SrF2 in 595 nm is a superposition of absorptions from two types of F2 centre, one oriented along (100) and the other along (110).
Abstract: It is suggested that a broad absorption band which occurs in additively coloured CaF2 at 521 nm and in additively coloured SrF2 at 595 nm is a superposition of absorptions from two types of F2 centre, one oriented along (100) and the other along (110). Broad emission bands of the two types of centre are also superimposed, peaking in CaF2 at 585 nm and in SrF2 at 644 nm. Under high resolution a zero phonon line of the (110) oriented F2 centre is observed at 20K in both emission and absorption bands; it occurs in CaF2 at 539.6 nm and in SrF2 at 605.3 nm, The excitation spectra for both the zero phonon line emission and the broad band emission have been investigated and their polarization properties established. Both the zero phonon line and the broad absorption band may be made dichroic by bleaching with linearly polarized light at 77K; this treatment produces preferential alignment of the centres. The destruction of the dichroism by thermally induced disorientation has been studied. Optical pumping gives rise to a reduction of intensity of absorption of F2 centres due to population of metastable excited states; the lifetimes of these states have been measured. Uniaxial stress measurements on the zero phonon lines show that the centres involved have orthorhombic I symmetry and that the dipole moment of the transition is along (100). The zero phonon lines also show a large linear Stark effect. From the combined stress and Stark measurement it follows that the point symmetry of the centres giving rise to the zero phonon lines is C2v.
TL;DR: The mode of orientation of RF molecules suggests appearance of some type of binding between RF and the PVA matrix, and transition moments of absorption bands are intermediate in direction between long and short axes of the RF molecule.
Abstract: — The dichroism and anisotropy of emission of polyvinyl alcohol (PVA) film with riboflavin (RF) were measured. The short axis of the RF molecule seems to be oriented in the direction of stretching of the film. The transition moment of the weak absorption band at 300 nm is also parallel to this direction, but it forms an angle greater than 50° with the emission oscillator. The transition moments of absorption bands at 440, 360 and 270 nm are intermediate in direction between long and short axes of the RF molecule. The extinction at 360 nm probably involves more than one electronic transition. Angles between absorption oscillators are very close to those obtained by Song and Kurtin. The mode of orientation of RF molecules suggests appearance of some type of binding between RF and the PVA matrix.
TL;DR: A number of mixed ligand complexes of rare earth ions La3+, Pr3+, Nd3+, Sm3+, Eu3+, Tb3+, with salicylaldehyde as the valence neutralising ligand and phenenthroline, bipyridine, quinoline and pyridine as neutral ligands have been synthesized and their composition established.
TL;DR: The efficiency of energy transfer from Chl b to Chl a, derived from data, was found to depend on the wavelength of exciting light, which is tentatively explained as evidence of superposition of a "fast" energy transfer upon the "delayed" transfer, which takes place after vibrational equilibration.
TL;DR: In this paper, a new color center has been observed in neutron-irradiated crystals of calcium oxide doped with magnesium, and it is proposed that this defect is an FA+ center, an interpretation supported by a comparison of its properties with those of the F+ centre.
Abstract: A new colour centre has been observed in neutron-irradiated crystals of calcium oxide doped with magnesium. It has an absorption band peaking at 374 nm and a complementary emission band at 398 nm. A zero-phonon line appears at 384.5 nm in absorption and emission. The value of the Huang-Rhys factor for both bands is S approximately=4. The defect cannot be detected in absorption in irradiated pure crystals, but the zero-phonon line has been detected weakly in emission. The line is shifted to the blue and broadened in the doped crystals compared with the pure crystals. A similar shift and broadening occurs for the F+ centre zero-phonon line. These effects can be understood in terms of internal strains caused by the magnesium impurities. Uniaxial stress experiments show that the new centre has tetragonal symmetry, the absorption and emission bands having electric dipole transition moments parallel to the fourfold axis. It is proposed that this defect is an FA+ centre, an interpretation supported by a comparison of its properties with those of the F+ centre.
TL;DR: In this article, the absorption of undoped ZnTe crystals was measured in the photon energy region from visible wavelegth to 15 µm, at the temperature from 77 to 520 K. This absorption band is attributed to the electronic transitions from the splitoff-valence band to the shallower and deeper acceptor levels, most likely due to Zn vacancy.
Abstract: Optical absorption in undoped ZnTe crystals grown by Piper-Polich method is measured in the photon-energy region from visible wavelegth to 15 µm, at the temperature from 77 to 520 K. In the crystal grown in vacuum, a broadband absorption is observed in the photon-energy region 0.9 to 1.4 eV. It is found that this absorption band consists of a peak and a shoulder at 77 K. This absorption band is attributed to the electronic transitions from the split-off-valence band to the shallower and deeper acceptor levels, most likely due to Zn vacancy. By analyzing the experimental results, the energies of the acceptor levels are estimated to be 0.06 and 0.16 eV above the top of the valence band, and the radii of the acceptor states to be 9.5 and 6.5A, for a shallower and deeper acceptor states, respectively. The spin-orbit splitting at the \varGamma point is determined to be 0.95 eV.