Chemistry of the CARBOFTOREX process. Identification of the absorption bands of the ligands in the electronic spectra of aqueous solutions of U(VI) fluoride carbonate complexes

The electronic absorption bands of U(VI) fluoride carbonate and fluoride hydroxide complexes were assigned taking account of dissociation, hydration, association, and ligand exchange. The absorption in the range of 190–400 nm was found to be related to the formation of neutral and dissociated anionic U(VI) fluoride carbonate and fluoride hydroxide complexes and the polynuclear Na_2n [(UO₂–O–UO₂)F₄(OH)_2n–1 ? kH₂O] complex.     

Chemistry of the CARBEX process. Identification of the absorption bands of the ligands in the electronic spectra of U(VI) extracts with methyltrioctylammonium carbonate

The electronic absorption bands of extracts of the Na₄[UO₂(O₂)(CO₃)₂] complex with methyltrioctylammonium (MTOA) carbonate were assigned taking into account hydration, hydrolysis, dissociation, polymerization, and ligand exchange, which occur in aqueous and organic solutions. It was shown that the extractable compound, (R₄N)₄[UO₂(O₂)(CO₃)₂], present in low concentrations in the organic phase partly dissociates by one step to give the (R₄N)₃[UO₂(O₂)(CO₃)₂]^– anions, while at high concentrations, it is converted to polynuclear complex.     

Analysis of composite bands in the electronic absorption spectra of compounds in solutions

Appearance of composite bands consisting of two individual bands with different half-widths in the course of resolution of absorption spectra was analyzed.     

On composite bands in the electronic absorption spectra of coordination compounds in solutions

Appearance of composite bands in resolved electronic absorption spectra was analyzed. Criteria for diagnostics of such bands, as well as a technique for their possible resolution into individual bands, were formalized and described.     

Computer simulation of the shape of absorption bands in electronic spectra ofJ-aggregates

The shape of absorption bands of aggregates formed by two, four, and nine molecules of a polymethine dye was calculated by the Monte-Carlo method. The energy of interaction of the molecules in the ground state was simulated using atom-atom potentials, and the energies of interaction between dipole moments of electronic transitions of the monomers were estimated by quantum-chemical methods. In the dimer aggregate the dipole moments of the electronic transitions in the monomers interact weakly; therefore, the electron absorption spectrum should be similar to that of the monomer. On going from the dimer to the aggregates consisting of four and nine monomers, the relative positions of monomers change and this, in turn, increases the energy of interaction between the dipole moments of their electronic transitions, resulting in a red shift characteristic ofJ-aggregates and narrowing of the absorption bands. Translated fromIzvestiya Akademii Nauk Seriya Khimicheskaya. No. 1, pp. 67–69, January, 1997.     

The nature of the bands of the electronic absorption spectra of acid solutions of aromatic α,β-unsaturated ketones

The electronic absorption spectra of 34 unsaturated ketones were measured in solutions of 93% sulfuric acid. The curves of the absorption of the hydroxycarbonium ions formed as a result of protonation of the investigated compounds in sulfuric acid solutions, are characterized by the presence of two intense bands of the -^* type in the region of 330–630 nm. The nature of the bands of the investigated compounds is discussed on the basis of the calculated data, obtained according to the PPP method, with an estimation of the localization and charge transfer numbers of the electronic transitions on individual fragments. According to the data of calculation and graphical analysis it was shown that the long-wave band in a series of derivatives of diphenylmethane and diphenyl oxide (I, II) should be assigned to the protonated cinnamoyl (C) fragment, while the second (short-wave) band should be assigned to the protonated acetophenone (A) fragment. The long-wave band in the series of derivatives of diphenyl sulfide, diphenylamine, and N-methyldiphenylamine (III–V) was assigned to the protonated acetophenone fragment. The resonance, dipole-dipole and exchange interactions of the fragments A and C is analyzed, and an attempt was undertaken to distinguish various types of interactions.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 3, pp. 321–328, May–June, 1985.     

Chemistry of the CARBEX process: Identification of absorption bands of the ligands in the electronic spectra of aqueous solutions of Na<Subscript>4</Subscript>[UO<Subscript>2</Subscript>(CO<Subscript>3</Subscript>)<Subscript>3</Subscript>]

On the basis of consideration of hydration, hydrolysis, dissociation, polymerization, and ligand exchange that occur in aqueous solutions of U(VI) complexes, a new approach to the assignment of absorption bands of the ligands in electronic spectra of uranium(VI) carbonate complexes in the range 190–400 nm has been suggested. For the Na₄[UO₂(CO₃)₃] complex, the following assignment of absorption bands has been made: Na₃[UO₂(CO₃)₃]^–, 258 nm; Na₂[UO₂(CO₃)₃]^2–, 300 nm; and Na₄[UO₂(CO₃)₃], 330 nm.     

Dependence of the electronic absorption spectra of aqueous solutions of iodine monochloride on the conditions of dilution and storage time

The electronic absorption spectra of aqueous solutions of iodine monochloride ICl are studied. The spectra of as-prepared solutions display the absorption band associated with hydrated ICl molecules. An additional band indicating that molecular iodine was formed in the solution emerges in the spectrum as dissolution takes place. Only the band belonging to iodine monochloride remains in the absorption spectra, and no additional bands appear after chloride anions Cl^? are added to the solution. The absorption spectrum becomes more complex when ICl is dissolved in an alkaline medium. The band belonging to molecular iodine emerges in the spectra at low alkali concentrations, while being transformed to other shorter-wavelength bands at high alkali concentrations (рН ≥ 12).     

Line shapes in electronic absorption spectra. Phenanthrene

The 3000 Å, (¹B₂ ← ¹A₁), absorption system of phenanthrene in durene crystals at 4°K illustrates an electronic transition, which is subject to near-resonance vibronic perturbations whose effect is intermediate to both the small (sparse intermediate) and large molecule (statistical) limits. Both broad (300 cm^?1) and narrow (10 cm^?1) lines are evident. A model is proposed which incorporates both these features by fast allowing for a consideration of the interaction between a small number of discrete levels, those associated with the largest coupling, followed by a treatment of the broadening of these levels through interaction with the remaining near continuum of states of the lower electronic state. Thus, one and the same electronic state provides both a sparse and dense manifold of levels. An important result of the model is that in terms of absorption intensities all the lines emerge with the same heights but differ in widths. When the intensities are summed with respect to energies this aspect is obscured. This approach has been shown to satisfactorily reproduce many of the features of the ¹B₂ absorption spectra of phenanthrene and phenanthrene-d₁₀. The ¹B₂ absorption systems have also been measured in the vapour phase and fine structure attributable to vibronic coupling and sequence band development are discussed.     

Theoretical study of absorption and fluorescence spectra of firefly luciferin in aqueous solutions

The absorption and fluorescence spectra of firefly luciferin, which is an analog of oxyluciferin, are investigated by performing the density functional theory (DFT) calculations, especially focusing on the experimentally unassigned peaks. Time-dependent DFT calculations are performed for the excited states of firefly luciferin and its conjugate acids and bases. We find that (1) the peaks in the experimental absorption spectra correspond to the excited states of not only (6'O(-), 4COO(-)) and (6'OH, 4COO(-)), but also (6'OH, 4COOH) and (6'OH, 3H(+), 4COOH); (2) the peaks in the experimental fluorescence spectra correspond to the excited states of not only (6'O(-), 4COO(-)), but also (6'OH, 4COO(-)), (6'O(-), 4COOH), (6'OH, 4COOH) and (6'OH, 3H(+), 4COOH); (3) the unassigned peak near 400 nm in the experimental absorption spectra at pH 1 is assigned to the absorption from the equilibrium ground state to the first excited state of (6'OH, 3H(+), 4COOH); and (4) the unassigned peak at 610 nm in the experimental fluorescence spectra corresponds to the transition from the equilibrium first excited state to the ground state of (6'OH, 4COO(-)).     

The vibronic and raman spectra of the uranyl ion in anhydrous hydrogen fluoride

The vibronic spectrum of the UO₂²⁺ cation in HF-AsF₅ solution has been recorded in the range 340–450 nm and is much better resolved than corresponding aqueous spectra.     

Chemistry of the CARBEX process: Identification of absorption bands of the ligands in the electronic spectra of aqueous solutions of Na<Subscript>4</Subscript>[UO<Subscript>2</Subscript>(O<Subscript>2</Subscript>)CO<Subscript>3</Subscript>)<Subscript>2</Subscript>]

On the basis of consideration of dissociation, hydration, association, and ligand exchange, the assignment of absorption bands in the electronic spectra of aqueous solutions of the Na₄[UO₂(O₂)CO₃)₂] complex has been performed. It has been demonstrated that the absorption in the range 190–400 nm is caused by the oxygen atoms of the O₂^2- and CO₃^2- groups and hydration water molecules of dissociated and neutral complex species Na₃[UO₂(O₂)(CO₃)₂]^–, Na₂[UO₂(O₂)(CO₃)₂]^2–, and Na₄[UO₂(O₂)(CO₃)₂].     

Electronic structure and nature of the bands in electronic absorption spectra of stable phenoxyl radicals of indophenoxyl and galvinoxyl

On the basis of results from quantum chemical calculations, made using the CNDO/S approximation method and taking into account configurational interaction, it has been shown that the first long-wave and subsequently more intense bands in the electronic absorption spectra of the phenoxyl radicals indophenoxyl and galvinoxyl are due to ^* electron transfers. The bands related to the p^* electron transfers of unshared p-electron pairs of oxygen and nitrogen atoms are located between them. It is suggested that displacement of the spectrum bands into the red region in transferring from the indophenoxyl to the galvinoxyl radical is caused by a reduction of the electron acceptor capacity of the bridging atom between the phenoxyl groups of the radical.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 6, pp. 737–740, November–December, 1987.     

IR spectra of hydrogen fluoride solutions in n-propanol

The densities of solutions of HF in n-PrOH were measured at different mole ratios of the components (from 1 : 12 to 3 : 1), and their IR spectra were recorded. The spectra of all the solutions exhibit absorption bands at 3500, 2600, and 1800 cm^–1 and continuous absorption (CA) in the frequency range from 3500 to 1300 cm^–1. The intensities of these bands and CA increase in proportion to the concentration of HF in solution. The difference between the experimental solution density and the calculated additive sum of the densities of the solution components behaves analogously. The formation of heterocomplexes with a stoichiometric ratio greater than 3 : 1 in the HF solutions in propanol was revealed. These heterocomplexes have large identical structural fragments with the strong quasi-symmetric H-bond. The results of calculations of the stretching vibration frequencies and relative stability of different cyclic pentamers suggest that such a fragment is the most stable cyclic heteropentamer, (HF)₂(nPrOH)₃, in which the HF molecules occupy the neighboring positions.