Electronic absorption spectra of 5- and 6- fluoroindoles

The electronic absorption spectra of 5-and 6-fluoroindoles, corresponding to the λ2850 Å system of indole, have been recorded in the vapour phase and analysed, assuming C_s symmetry for the molecules. The observed band system in both the molecules which lies in the region λ3100–2680 Å has been identified as a π* ← π transition corresponding to a ¹A′ ← ¹A′ transition. The i.r. spectra of these molecules have also been recorded and analysed and the results are used in the analyses of the electronic spectra. These show that there is not much change in the shape and very little change in size of either of these molecules in the excited electronic states.     

Electronic absorption spectra of 2,3- and 2.5-dimethylpyrazines

The electronic absorption spectra of 2,3- and 2,5-dimethylpyrazines were recorded and analysed considering C_2ν and C_2h symmetry for the molecules, respectively. Vibrational analysis of the electronic spectra of these molecules has shown the existence of a vibronic interaction between two electronic states of both the molecules through an out-of-plane bending mode.     

Electronic and vibrational spectra of 2,4,6-trichloro- and 6-chloro-2,4-dimethoxypyrimidine

This paper presents the investigations of the electronic and vibrational spectra of 2,4,6-trichloropyrimidine and 6-chloro 2,4-dimethoxypyrimidine. The electronic spectra have been recorded in the liquid and vapour states in the region 50000-28000 cm⁻¹. Then-π and π-π transitions are classified in each case. Infrared absorption spectra of 2,4,6-trichloropyrimidine in nujol have been recorded in the region 4000-400 cm⁻¹. It is concluded that substituents like Cl or OCH₃ do not have much influence on thesp ² electron of the nitrogen atom of the ring. From infrared studies the mass-dependent modes and the modes insensitive to substitution have been pointed out. The assignments are tentative and are based on the group frequency approach and data available for similar molecules.     

Electronic structure of the spinel Li4Ti5O12 studied by ab initio calculations and X-ray absorption spectroscopy

The electronic structure of the spinel compound Li₄Ti₅O₁₂, used as anode material in Li-ion batteries, is studied both theoretically and experimentally. The partial densities of occupied and vacant s, p and d electronic states were calculated for Li, Ti and O, using the linear augmented plane wave formalism (LAPW) in order to obtain information on the chemical bond. X-ray absorption spectra were recorded at the Ti L₂₃, Ti K and O K absorption edges and calculated within the dipolar approximation by considering both the electronic ground state and the effect of core holes. The atomic origin of the observed main peaks is analysed from the comparison between the experimental and calculated spectra. We show that the two types of lithium in Li₄Ti₅O₁₂ which are found in tetrahedral and octahedral sites could be distinguished by X-ray absorption spectroscopy. We suggest to use such a technique for the investigation of Li-insertion mechanisms in lithium titanate spinels.     

DFT assessment of the spectroscopic constants and absorption spectra of neutral and charged diatomic species of group 11 and 14 elements

The spectroscopic constants and absorption spectra of neutral and charged diatomic molecules of group 11 and 14 elements formulated as [M₂]^+/0/? (M = Cu, Ag, Au), and [E₂]^+/0/? (E = C, Si, Ge, Sn, Pb) have been calculated at the PBE0/Def2‐QZVPP level of theory. The electronic and bonding properties of the diatomics have been analyzed by natural bond orbital analysis approach and topology analysis by the atoms in molecules method. Particular emphasis was given on the absorption spectra of the diatomic species, which were simulated by time‐dependent density functional theory calculations employing the hybrid Coulomb‐attenuating CAM‐B3LYP density functional. The simulated absorption spectra of the [M₂]^+/0/? (M = Cu, Ag, Au) and [E₂]^+/0/? (E = C, Si, Ge, Sn, Pb) species are in close resemblance with the experimentally observed spectra whenever available. The neutral M₂ and E₂ diatomics strongly absorb in the ultraviolet region, given rise to UVC, UVA and in a few cases UVB absorptions. In a few cases, weak absorbion bands also occur in the visible region. The absorption bands have thoroughly been analyzed and assignments of the contributing principal electronic transitions associated to individual excitations have been made. © 2014 Wiley Periodicals, Inc.     

Infrared and electronic absorption spectra of some trisubstituted benzenes

The electronic absorption spectra of 2,3-, 2,4-, 2,5-, 2,6- and 3,4-difluorobenzonitriles, 3,4-difluoroaniline and 3,4-difluoroanisole in the ultraviolet region in vapour phase have been recorded on medium quartz and Hilger large quartz spectrographs and on a Hitachi model 150-20 UV-VIS ratio recording spectrophotometer. All the molecules investigated have exhibited two π* ← π band systems corresponding to ¹B_2u ← ¹A_1g (λ2600 Å) and ¹B_1u ← ¹A_1g (λ2100 Å) systems of benzene. The infrared absorption spectra of all the molecules studied have also been recorded and analysed. These infrared data have been taken to help analyse the u.v. spectra of the molecules studied.     

Extension of High‐Resolution Optical Absorption Spectroscopy to Divalent Neodymium: Absorption Spectra of Nd2+ Ions in a SrCl2 Host

There is a lack of information on electronic spectra of divalent neodymium, and thus the synthesis and characterization of Nd²⁺ systems is now reported. Stabilization of neodymium is observed in a chloride host, which importantly has been accomplished with Nd ions introduced in a divalent state during synthesis, unlike by γ‐irradiation of Nd³⁺ system employed previously. This method yields good‐quality SrCl₂:Nd²⁺ single crystals. For the first time the electronic absorption spectra of Nd²⁺ doped in SrCl₂ have been recorded with high resolution at liquid helium temperature (4.2 K). Identification of the absorption bands occurring in the spectral range of 5000–40 000 cm⁻¹ (2000–250 nm) has been achieved and their tentative assignment proposed. This uniquely detailed Nd²⁺ absorption spectrum provides basis for fingerprinting method enabling identification of the presence of Nd²⁺ ions in future spectra as well as in existing but as‐yet not fully resolved spectra.     

Electronic absorption spectra of some azo compounds with condensed ring systems in non-aqueous and mixed buffer solvents

The electronic absorption spectra of eight substituted phenylazo derivatives of α-and β-naphthol, 9-phenanthrol and 5- and 6-chrysenol were studied in different organic solvents. The assignment of the spectral bands obtained and also the effect of organic solvents on the colour of the compounds was investigated. The spectra in buffer solution over the pH range 2–14 were recorded and explained; also the pK_a values were determined.     

Isolation, Purification and Spectral Characteristics of Soluble Guanylate Cyclase from Bovine Lung *

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The IR Absorption Spectra of Aqueous Solutions of Dimethylsulfoxide over the Frequency Range 50–300 cm−1 and the Mobility of Water Molecules

The IR absorption spectra of aqueous solutions of dimethylsulfoxide (DMSO) with concentrations from 100% H₂O to 100% DMSO were recorded over the frequency range 50–500 cm^?1. The absorption spectra were described using the theoretical scheme of hindered rotators. A model was developed according to which orientation relaxation in solution was related to separate rotations of H₂O and DMSO molecules through fixed small and (or) large angles in a unified network of H-bonds consisting of several subsystems ordered to various degrees. The calculated absorption spectra were in agreement with the experimental data in the far IR region. Elementary motions of molecules were found to slow down in the passage from pure dimethylsulfoxide to its aqueous solutions. The special features of the hydrophilic and hydrophobic hydration of DMSO polar and nonpolar groups were considered.     

Spectroscopic studies of conducting polymers

Electronic and vibrational spectra of poly(p-phenylenevinylene) doped with donors or acceptors have been studied, together with the spectra obtained for the radical ions and divalent ions of its oligomers. The electronic absorption spectra of doped poly(p-phenylenevinylene) in the region from visible to near-infrared show two bands for the H₂SO₄-doped species and one very broad band for the Na-doped species. On the basis of the analyses of resonance Raman spectra, the two electronic absorption bands of the H₂SO₄-doped species are attributed to a polaron-lattice structure, whereas the broad band of the Na-doped species is attributed to overlapping absorptions associated with localized electronic levels of polarons and bipolarons. A Pauli spin susceptibility of the H₂SO₄-doped species is explained by the polaron-lattice structure.     

Time‐dependent density functional theory studies of the electronic absorption spectra of metallophthalocyanines of group IVA

Time‐dependent density functional theory (TD‐DFT) calculations were carried out in a comparative study of the electronic absorption spectra of lead(II) phthalocyaninate (PbPc), tin(II) phthalocyaninate (SnPc), tin(IV) dichlorophalocyaninate (PcSnCl₂), germanium(II) phthalocyaninate (GePc), and germanium (IV) dichlorophalocyaninate (PcGeCl₂) with the B3LYP method and LANL2DZ basis set. Our calculated bands correspond well with the experimental results. The electronic natures of all the bands in the absorption spectra are assigned and analyzed comparatively according to the calculated electronic transition contributions. With the increase of the dielectric constant from CHCl₃ to DMSO, all the electronic absorption bands are somewhat red shift, consistent with the shift rules measured experimentally. The radius of the central metals has great influence to the absorption spectra, especially for the B bands. The influence of the radius of the central metals to the absorption spectra of PcSnCl₂ and PcGeCl₂ is smaller than to the spectra of the nonplanar MPcs (M = Pb, Sn, and Ge). Axial ligands also greatly changed the electronic absorption spectra due to the change of the orbital energy level and the molecular symmetry. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Electronic structure of the diaquabis(hydrogen malato) copper(II) crystal

Summary The electronic absorption and e.s.r. spectra of a crystal of the title compound [Cu(H₂O)₂ (C₄H₅O₅)₂] were recorded and experimental results are discussed quantitatively, using ligand field theory and the radial wave function of bound Cu^II. The electronic structure of the compound is consistent with its crystal structure.     

Spectrophotometric study of 5-arylidene- and 5-(5-arylfurfurylidene)rhodanines

5-Arylidenerhodanines and the previously undescribed 5-[5-(4-R-phenyl)furfurylidene]rhodanines were synthesized by the Andreasch method. It is assumed that Fermi resonance appears in the IR spectra of some of these compounds in the region of carbonyl absorption; bands of associated N-H bonds were identified. It is shown that in the case of 4-N(CH₃)₂-benzylidenerhodanine the long-wave band in the electronic spectra is a bathochromically shifted band of the same nature as the band in the spectra of 5-arylidenerhodanine derivatives with weak donor groups. The introduction of an arylfurfurylidene grouping gives rise to a substantial bathochromic shift of the absorption band of their molecules.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1490–1494, November, 1977.     

X-ray absorption and resonant Auger spectroscopy of O2 in the vicinity of the O 1s-->sigma* resonance: experiment and theory

We report on an experimental and theoretical investigation of x-ray absorption and resonant Auger electron spectra of gas phase O(2) recorded in the vicinity of the O 1s-->sigma(*) excitation region. Our investigation shows that core excitation takes place in a region with multiple crossings of potential energy curves of the excited states. We find a complete breakdown of the diabatic picture for this part of the x-ray absorption spectrum, which allows us to assign an hitherto unexplained fine structure in this spectral region. The experimental Auger data reveal an extended vibrational progression, for the outermost singly ionized X (2)Pi(g) final state, which exhibits strong changes in spectral shape within a short range of photon energy detuning (0 eV>Omega>-0.7 eV). To explain the experimental resonant Auger electron spectra, we use a mixed adiabatic/diabatic picture selecting crossing points according to the strength of the electronic coupling. Reasonable agreement is found between experiment and theory even though the nonadiabatic couplings are neglected. The resonant Auger electron scattering, which is essentially due to decay from dissociative core-excited states, is accompanied by strong lifetime-vibrational and intermediate electronic state interferences as well as an interference with the direct photoionization channel. The overall agreement between the experimental Auger spectra and the calculated spectra supports the mixed diabatic/adiabatic picture.     

NH-tautomerism effects and isocyclic substitution in alkylporphyrins and their chemical dimers

A study has been made of the absorption spectra, circular dichroism in a magnetic field (MCD), and polarized fluorescence of individual NH-tautomers of free-base porphyrins with asymmetric substitution. The four-orbital model of Gouterman and the perimeter model of Michl have been used in demonstrating that, in spite of the basic differences in type of electronic spectra of the two NH-tautomers of each compound, their absorption spectra in the visible region are described by a system of two linear oscillators X and Y. The fluorescence polarization spectra of the tautomers in the region of band III are extremely sensitive to changes in the side substituents in the isocycle. From an analysis of the sign sequence of electronic bands in the MCD spectra, it has been established that these compounds may be classed as hard chromophores with identical type of orbital splitting for the HOMO (b₁ and b₂) and LUMO (c₂ and c₂) in the two tautomers of one and the same compound. A specific role has been found for the keto group in the isocycle, as manifested in inversion of the sign sequence of electronic bands in the MCD spectra of NH-tautomers with a cyclopentanone ring.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 3, pp. 295–305, May–June, 1989.     

Spin-orbit Splitting and Lifetime Broadening in the A2Δ Electronic State of l-C5H

Optical absorption bands at ～18772 and ～18807 cm^-1, previously assigned to A²Δ-X2Π electronic origin band transitions of the linear carbon-chain radicals C₅H and C₅D, respec-tively, have been reinvestigated. The spectra have been recorded in direct absorption apply-ing cavity ring-down spectroscopy to a supersonically expanding acetylene/helium plasma. The improved spectra allow deducing a l-C₅H upper state spin-orbit coupling constant A'=-0.7(3) cm^-1 and a A²Δ lifetime of 1.6±0.3 ps.     

Characterization of SiN and other transient species in a silicon tetrachloride–nitrogen discharge

Infrared diode laser absorption spectroscopy has been used to detect the A–X electronic spectrum of diatomic SiN in a SiCl₄/N₂ plasma. The intensity of the SiN transitions with respect to the ratio of SiCl₄:N₂ flow rate was investigated. A correlation between intense signals of SiN and the optimal growth conditions for a-SiN films reported in literature was found. This observation lends support to the importance of diatomic SiN as a film precursor. The electronic emission spectra of silicon-containing transient species were also recorded in the plasma. A brief discussion of the plasma reaction pathways of SiN is presented.     

Inner- and valence-shell excitation of SF4 studied by photoabsorption and electron energy loss spectroscopy

The S 1s photoabsorption spectrum of SF₄ recorded with synchrotron radiation is reported along with the electron energy loss spectrum of SF₄ in the regions of S 2p, S 2s and F 1s excitation recorded under dipole dominated conditions. The electron energy loss spectrum of SF₄ in the region of valence electron excitation is also reported. All of these spectra are interpreted in terms of a common manifold of upper levels which includes valence levels whose term values reflect the different axial and equatorial SF bond lengths in this molecule. The spectra are good examples of the effects of potential barriers on electronic excitation spectra.     

FT-IR, FT-Raman, ab initio and DFT structural, vibrational frequency and HOMO-LUMO analysis of 1-naphthaleneacetic acid methyl ester

In this work, the FT-IR and FT-Raman spectra of 1-naphthaleneacetic acid methyl ester (abbreviated as 1-NAAME, C₁₀H₇CH₂CO₂CH₃) have been recorded in the region 3600–10 cm⁻¹. The optimum molecular geometry, normal mode wavenumbers, infrared and Raman intensities, Raman scattering activities, corresponding vibrational assignments, Mullikan atomic charges and other thermo-dynamical parameters were investigated with the help of HF and B3LYP (DFT) method using 6-31G(d,p), 6-311G(d,p) basis sets. Reliable vibrational assignments were made on the basis of total energy distribution (TED) calculated with scaled quantum mechanical (SQM) method. From the calculations, the molecules are predicted to exist predominantly as the C1 conformer. The correlation equations between heat capacity, entropy, enthalpy changes and temperatures were fitted by quadratic formulae. Lower value in the HOMO and LUMO energy gap explains the eventual charge transfer interactions taking place within the molecule. UV–VIS spectral analyses of 1NAAME have been researched by theoretical calculations. In order to understand electronic transitions of the compound, TD-DFT calculations on electronic absorption spectra in gas phase and solvent (DMSO and chloroform) were performed. The calculated frontier orbital energies, absorption wavelengths (λ), oscillator strengths (f) and excitation energies (E) for gas phase and solvent (DMSO and chloroform) are also illustrated.