The mechanism and kinetics of energy transfer processes in the Xe–CCl4–M (M=CH4, C2H2, C2H4, C2H6 C3H6 and C3H8) mixtures irradiated by xenon resonance light

The mechanism and kinetics of energy transfer from Xe(6s[3/2]₁) resonance state (E=8.44 eV) to selected hydrocarbon molecules have been investigated by XeCl(B–X) (λ_max=308 nm) fluorescence intensity measurements at stationary conditions in Xe–CCl₄–M systems. Steady-state analysis of the fluorescence intensity dependence on the xenon and M pressure at constant CCl₄ concentration shows that these process occur in the two- and three-body reactions: Xe(6s[3/2]₁⁰)+M→products, Xe(6s[3/2]₁⁰+M+Xe→products. The two- and three-body rate constants for these reactions have been found (see Table 1Table 1. Experimental parameters of Eq. (8)found by least square method in Xe–CCl₄–C₂H₂ and Xe–CCl₄–C₂H₄ systems for chosen xenon pressures in the range 25–150 Torr. Linear correlation coefficients (R) are also shown     

2.

Pulse radiolysis study of energy transfer processes in Xe–M mixtures (M=CH2F2,CHF3,CHF2Cl,CHFCl2 and CF3Cl)     

《Radiation Physics and Chemistry》1999,53(4):417-424

The time-resolved spectroscopy measurements were used to study the kinetics of energy transfer process in the pulse radiolysis of xenon- fluoro- and chlorofluoromethanes mixtures. The main channel, at xenon pressure above 40 Torr, seems to be of third order, while at lower xenon pressures the second order process was the main one.     

3.

Photoionization of Xe2, Xe3 and Xe4 in the 1024–1113 Å region     

Y. Lu  Y. Morioka  T. Matsui  T. Tanaka  H. Yoshii  R. I. Hall  K. Ito  T. Hayaishi 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1995,35(2):125-129

The mass spectra of Xe _n ⁺ clusters (n=2–13) were recorded using a supersonic beam and an ion time-of-flight mass analyser. The yield of Xe ₂ ⁺ , Xe ₃ ⁺ and Xe ₄ ⁺ cluster ions was measured with a resolution of 0.1 Å (1 meV) in the 1024–1113 Å (11.1–12.1 eV) region. Autoionizing Rydberg series of Xe₂ converging to theC ²_3/2u state of Xe ₂ ⁺ were observed in the spectrum of Xe ₂ ⁺ . The photoionization yield of Xe ₃ ⁺ and Xe ₄ ⁺ ions each displayed similar broad features that contained no fine structure corresponding to vibrational states. The broad features were assigned to autoionizing Rydberg series by analogy with the dimer ion spectrum.     

4.

Ab initio study of electronic energy transfer in the quenching of CO*(a 3Π) by H2     

《Chemical physics letters》1987,142(5):359-365

Potential energy calculations for the interaction of CO(a ³Π) with H₂(X ¹Σ_g⁺) are presented, both at the MC SCF level and with the inclusion of extensive configuration interaction. In C_2v geometry, the lowest two ³B₂ surfaces exhibit a strongly avoided crossing. At the highest level of theory used, the lowest surface provides a barrier-free adiabatic pathway for energy transfer from CO(a) to H₂, the products being CO(X ¹Σ⁺) and H₂(b ³Σ_u⁺), which dissociates to two H atoms. The energy transfer occurs by a two-electron exchange mechanism.     

5.

Metal–metal charge transfer and interfacial charge transfer mechanism for the visible light photocatalytic activity of cerium and nitrogen co-doped TiO2     

Rajashekhar K. Eraiah  Giridhar Madras 《Journal of Sol-Gel Science and Technology》2014,71(2):193-203

Nanosized cerium and nitrogen co-doped TiO₂ (Ce–TiO_2?xN_x) was synthesized by sol gel method and characterized by powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), FESEM, Fourier transform infrared, N₂ adsorption and desorption methods, photoluminescence and ultraviolet–visible (UV–vis) DRS techniques. PXRD analysis shows the dopant decreases the crystallite sizes and slows the crystallization of the titania matrix. XPS confirm the existence of cerium ion in +3 or +4 state, and nitrogen in ?3 state in Ce–TiO_2?xN_x. The modified surface of TiO₂ provides highly active sites for the dyes at the periphery of the Ce–O–Ti interface and also inhibits Ce particles from sintering. UV–visible DRS studies show that the metal–metal charge transfer (MMCT) of Ti/Ce assembly (Ti⁴⁺/Ce³⁺ → Ti³⁺/Ce⁴⁺) is responsible for the visible light photocatalytic activity. Photoluminescence was used to determine the effect of cerium ion on the electron–hole pair separation between the two interfaces Ce–TiO_2?xN_x and Ce₂O₃. This separation increases with the increase of cerium and nitrogen ion concentrations of doped samples. The degradation kinetics of methylene blue and methyl violet dyes in the presence of sol gel TiO₂, Ce–TiO_2?xN_x and commercial Degussa P25 was determined. The higher visible light activity of Ce–TiO_2?xN_x was due to the participation of MMCT and interfacial charge transfer mechanism.     

6.

Kinetics and mechanism of electron transfer processes in a hydrogen peroxide—trispicolinatoruthenate(II) system     

Olga Impert  Anna Katafias  Joanna Fenska  Przemys?aw Kita 《Transition Metal Chemistry》2012,37(1):7-16

Oxidation of trispicolinatoruthenate(II) complex by hydrogen peroxide leads to the formation of mer-trispicolinatoruthenium(III) in acidic or neutral solutions. Kinetics of the reaction were studied under a large excess of H₂O₂ at constant pH. The initial rate method gives a rate expression of the form: - d[\textRu(\textII)]/\textdt = k^II [\textH₂ \textO₂ ][\textRu(\textII)] - \hbox{d}[{\text{Ru}}({\text{II}})]/{\text{d}}t = k^{II} [{\text{H}}_{2} {\text{O}}_{2} ][{\text{Ru}}({\text{II}})] but the overall process examined till completion is far more complex. The rate of the reaction decreases with increasing pH to be practically completely retarded in alkaline media. The key step in the proposed reaction mechanism is the picolinato chelate ring opening followed by the substitution of the coordinated water by H₂O₂ and two-electron intramolecular ruthenium(II) oxidation. Formation of the final ruthenium(III) complex is assigned rather to the ruthenium(IV) reduction by H₂O₂ than ruthenium(II)–ruthenium(IV) comproportionation. The obtained results show the much slower rate of the trispicolinatoruthenate(II) oxidation by hydrogen peroxide or dioxygen than the mer-trispicolinatoruthenium(III) reduction by such bioreductants as cytochrome cII or some cobalt(II) reductants.     

7.

Noble-Gas Difluoride Complexes of MOF4 (M=Mo,W); Syntheses,Structures and Bonding of NgF2 ⋅ MOF4 and XeF2 ⋅ 2MOF4 (Ng=Kr,Xe)     

Mark R. Bortolus  Dr. Hélène P. A. Mercier  Dr. David S. Brock  Prof. Gary J. Schrobilgen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(15):e202103729

The NgF₂ ⋅ MOF₄ (Ng=Kr, Xe; M=Mo, W) and XeF₂ ⋅ 2MOF₄ complexes were synthesized in anhydrous HF (aHF) solvent and melts, respectively. Their single-crystal X-ray diffraction (SCXRD) structures show NgF₂ ⋅ MOF₄ and XeF₂ ⋅ 2MOF₄ have F_t−Ng−F_b- - -M arrangements, in which the NgF₂ ligands coordinate to MOF₄ through Ng−F_b- - -M bridges. The XeF₂ ligands of XeF₂ ⋅ 2MOF₄ also coordinate to F₃OM−F_b’- - -M'OF₄ moieties through Xe−F_b- - -M bridges to form F_t−Xe−F_b- - -M(OF₃)−F_b’- - -M'OF₄, where XeF₂ coordinates trans to the M=O bond and F_b’ coordinates trans to the M’=O bond. The Ng−F_t, Ng−F_b, and M- - -F_b bond lengths of NgF₂ ⋅ nMOF₄ are consistent with MOF₄ and F₃OM−F_b’- - -M'OF₄ fluoride-ion affinity trends: CrOF₄<MoOF₄<WOF₄≈F₃OMo−F_b’- - -Mo'OF₄<F₃OW−F_b’- - -W'OF₄. The [- -(F₄OMo)(μ₃-F)H- - -(μ-F)H- -]_∞ solvate was also synthesized in aHF and characterized by SCXRD. Quantum-chemical calculations show the M- - -F_b bonds of NgF₂ ⋅ MOF₄ and XeF₂ ⋅ 2MOF₄ are predominantly electrostatic, σ-hole type bonds.     

8.

Kinetics of CO2 absorption by aqueous mixtures of N,N′-diethylethanolamine and polyamines     

Elizabeth B. Joseph  Prakash D. Vaidya 《国际化学动力学杂志》2019,51(2):131-137

Aqueous solutions of N,Nʹ-diethylethanolamine (DEEA) are prospective high-capacity CO₂-capturing solvents. Their reactivity can be enhanced by promotion with absorption activators. Two polyamines were chosen as activators in this work, viz. (methylamino)propylamine (MAPA) and diethylene triamine (DETA). In a stirred cell reactor, kinetics of CO₂ absorption into aqueous DEEA/MAPA and DEEA/DETA mixtures was studied at 303 K. The molarity of DEEA was varied in the 2–2.5 M range, whereas the polyamine concentration was changed between 0.1 and 0.5 M. Pseudo–first-order rate constants were reported. Second-order rate constants for the CO₂ reactions with MAPA and DETA were determined too. DETA reacts faster than MAPA.     

9.

Rate constants for reactions of Cl abstraction from CCl4 by CCl3CH2·CHR radicals and Br abstraction from CCl3CH2CHBrR (R=Bun, AcO, OCNC4H8, CN) by ·Re(CO)5 radicals     

R. G. Gasanov 《Russian Chemical Bulletin》2000,49(1):46-49

The rate constants for reactions of Cl abstraction from CCl₄ by CCl₃CH₂·CHR radicals and Br abstraction from CCl₃CH₂CHBrR (R=Buⁿ, AcO, OCNC₄H₈, CN) by·Re(CO)₅ radicals were determined by ESR spectroscopy using spin trapping technique. Replacement of H atoms at the C(β) atom by O or N atoms reduces the reactivity of the radicals in the reactions of Cl abstraction from CCl₄ by approximately an order of magnitude. The presence of two polar groups at the C(β) atom results in appreciable decrease in the strength of the C−Br bond in CCl₃CH₂CHBrR adducts. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 45–48, January, 2000.     

10.

Theoretical unimolecular kinetics for CH4 + M ⇄ CH3 + H + M in eight baths, M = He, Ne, Ar, Kr, H2, N2, CO, and CH4     

Jasper AW  Miller JA 《The journal of physical chemistry. A》2011,115(24):6438-6455

Ensembles of classical trajectories are used to study collisional energy transfer in highly vibrationally excited CH(4) for eight bath gases. Several simplifying assumptions for the CH(4) + M interaction potential energy surface are tested against full dimensional direct dynamics trajectory calculations for M = He, Ne, and H(2). The calculated energy transfer averages are confirmed to be sensitive to the shape of the repulsive wall of the intermolecular potential, with an exponential repulsive wall required for quantitative predictions. For the diatomic baths, the usual "separable pairwise" approximation for the interaction potential is unable to describe the orientation dependence of the interaction potential accurately, and the ambiguity in the resulting parametrizations contributes an additional uncertainty to the predicted energy transfer averages of 20-40%. On the other hand, the energy transfer averages are shown to be insensitive to the level of theory used to describe the intramolecular CH(4) potential, with a computationally efficient semiempirical tight binding potential for hydrocarbons performing equally well as an MP2 potential. The relative collisional energy transfer efficiencies of the eight bath gases are discussed and shown to be a function of temperature. The ensemble-averaged energy transferred in deactivating collisions <ΔE(d)> for each bath is used to parametrize a single-exponential-down model for collisional energy transfer in master equation calculations. The predicted decomposition rate coefficients for CH(4) agree well with available experimental rate coefficients for M = He, Ar, Kr, and CH(4). The effect of vibrational anharmonicity on the predicted rate coefficients is considered briefly.     

11.

Synthesis of Bi4Ti3O12 by high energy milling of Bi2O3–TiO2 (anatase) mixtures     

V. Berbenni  C. Milanese  G. Bruni  A. Girella  A. Marini 《Journal of Thermal Analysis and Calorimetry》2016,126(3):1507-1511

     

12.

Kinetics and mechanism of CH3Br,CHF2Br,and C2HF4Br photolysis in the presence of dioxygen under the action of λ = 253.7 nm light     

I. K. Larin  T. I. Belyakova  N. A. Messineva  A. I. Spasskii  E. M. Trofimova 《Kinetics and Catalysis》2014,55(5):549-555

The photolysis of CH₃Br, CHF₂Br, and C₂HF₄Br mixed with oxygen under radiation emitted by a bactericidal mercury lamp (radiation intensity maximum at λ = 253.7 nm) has been investigated. Oxygen was added in order to simulate natural conditions. A photolysis mechanism has been suggested, the corresponding model calculations have been carried out, and the calculated data have been compared with experimental data. The calculated absorption cross sections are in agreement with the literature, thus proving the validity of the mechanism suggested. The ratios between the rate constants of the reactions of the photolytically generated CH₃, CHF₂, and C₂HF₄ radicals with molecular bromine and oxygen have been determined.     

13.

Composition of Ar–Kr,Kr–Xe,and N2–Ar Clusters Produced by Supersonic Expansion of Gas Mixtures     

O. P. Konotop  S. I. Kovalenko  O. G. Danylchenko  V. N. Samovarov 《Journal of Cluster Science》2015,26(3):863-875

     

14.

The photolysis of the uranyl oxalate system—III photochemical behaviour,kinetics and mechanism in aqueous solution     

《Journal of Inorganic and Nuclear Chemistry》1977,39(7):1195-1199

The photochemical behaviour, kinetics and mechanism of the uranyl oxalate system, have been studied at 25°C and pH 4.5. The detectable ionic and molecular species after photolysis are UO₂²⁺, U(IV) and CO₂. Kinetic evidence for the participation of an uranyl oxalate (1:2) complex as the primary photo-activatable species, is reported. The suggested photolysis mechanism is in agreement with the quantitative and qualitative results of this investigation and shows similar tendencies to the mechanism suggested for the photolysis in strongly acidic (pH ≤ 1.7) solutions.     

15.

The kinetics,catalysis and inhibition of the Baeyer—Villiger reaction in the processes of liquid-phase oxidation of organic compounds     

A. L. Perkel  S. G. Voronina 《Russian Chemical Bulletin》2018,67(8):1321-1329

Literary data on kinetics, catalysis and inhibition of the oxidation reaction of carbonyl compounds with peroxy acids according to the Baeyer—Villiger reaction under aerobic liquidphase oxidation conditions have been considered and discussed. The main reaction channel involves a reversible formation of α-hydroxyperoxy ester and its rearrangement to an ester or a lactone. In the case of homolytic decomposition of α-hydroxyperoxy ester no esters are formed. At all steps the formation and transformation of α-hydroxyperoxy ester are catalyzed by carboxylic acids. The possibility of formation of the second intermediate, presumably dioxirane, is shown. Catalysts of the oxidation processes such as variable-valency metal salts influence the kinetics at all steps in the Baeyer—Villiger reaction. Inhibition of ester formation in the presence of cobalt and manganese salts is associated with catalysis of homolytic decomposition of peroxy acid and α-hydroxyperoxy ester.     

16.

Structural variability of nucleosomes detected by single-pair Förster resonance energy transfer: histone acetylation, sequence variation, and salt effects     

Gansen A  Tóth K  Schwarz N  Langowski J 《The journal of physical chemistry. B》2009,113(9):2604-2613

Nucleosomes were reconstituted from 170 bp long fragments of 5S rDNA and an optimal positioning sequence, the Selex 601, with recombinant histones. In free-solution single pair F?rster resonance energy transfer (spFRET) measurements of the distance between fluorescently labeled bases in the nucleosomal DNA, the samples exhibited structural diversity. The structural heterogeneity correlated with the stability of the complexes and depended on the DNA sequence and histone acetylation. The stability of the nucleosomes was assessed via dilution-driven disruption: histone acetylation decreased nucleosome stability. The spFRET experiments used a new approach for data acquisition and analysis that we term "deliberately detuned detection" (D3). This permits the separation of subpopulations in the samples even for the low-FRET regime characteristic for the linker-DNA labeled nucleosomes. Thus, it became possible to study in more detail histone acetylation- and salt-dependent structural variations using either end- or internally labeled DNAs on the nucleosome. We found that the distance distribution of the fluorophore pairs on the linker DNA ends was much more sensitive to histone acetylation or sequence variation than that of labels on the internal part of the DNA, which was more tightly associated with the histone core. spFRET on freely diffusing nucleosomes allows us therefore to localize the influence of histone modifications and DNA sequence variations on the nucleosome structure and dynamics.     

17.

Temperature dependence of vibrational energy transfer in liquids: VV relaxation of CO(ν = 1) by O2 in liquid Ar from 86 to 145 K     

《Chemical physics》1986,104(3):455-465

The rate constant for the energy transfer process

has been measured for CO and O₂ dilute in liquid Ar along the coexistence curve between 86 and 145 K. The results are compared to gas phase measurements of this rate constant over the same temperature range. The ratio of the rate constants in the two phases is compared to that predicted by an application of the isolated binary collision (IBC) model for energy trasnfer, which scales the energy transfer rate constants by the rate constants for binary collisions in the two phases. The theoretical predictions of the IBC model are that the liquid state energy transfer rate constant, k^ℓ, should be 30–60% greater than the gas phase energy transfer rate constant, k^g. The measured value of k^ℓ is, within the experimental error, equal to that for k^g. Possible reasons for the discrepancy are discussed.     

18.

Solvent effects on the kinetics of solvolysis of trans-dichlorobis (N-methylethylenediamine)cobalt(III) ion in water–propan-2-ol and water–acetonitrile mixtures     

El-Subruiti  Gehan Moustafa 《Transition Metal Chemistry》1997,22(1):33-38

First order solvolysis rates of the trans-dichlorobis (N-methylethylenediamine) cobalt(III) ion have been measured over a wide range of solvent compositions and temperatures in water–propan-2-ol and water–acetonitrile mixtures. The rate of solvolysis is faster in the former mixtures rather than the latter. Plots of log(rate constant) versus the reciprocal of the dielectric constant of the co-solvent, and also versus the Grunwald–Winstein Y-values are non-linear for both co-solvents; this non-linearity is derived from a large differential effect of solvent structure between the initial and transition states. However, extrema in the variation of enthalpy H and entropy S of activation correlate well with the extrema in physical properties of the mixtures which are related to changes in solvent structure. Linear plots of H versus S were obtained and the isokinetic temperature indicates that the reaction is entropy controlled. The application of a free-energy cycle shows that changes in solvent structure affect the pentacoordinated cobalt(III) ion in the transition state more than the hexacoordinated cobalt(III) ion in the initial state. In addition, the stabilizing influence of changes in solvent structure is greater in propan-2-ol–water mixtures than in acetonitrile–water mixtures, and the difference becomes greater as the mole fraction, x2 of the organic co-solvent increases.     

19.

Surface-enhanced Raman scattering of M2–pyrazine–M2 (M = Cu,Ag, Au): Analysis by natural perturbation orbitals and density functional theory functional dependence     

Masaya Miyamoto  Masahiko Hada 《Journal of computational chemistry》2020,41(17):1628-1637

Here, we propose a new method to analyze various electronic properties of molecules based on natural perturbation orbitals (NPOs). We applied the proposed method to chemical enhancement of the surface-enhanced Raman scattering (SERS) intensity of M₂–pyrazine–M₂ (M = Cu, Ag, Au) complexes. The SERS intensity can be effectively decomposed into the contributions of four NPO pairs (1σ–1σ*, 2σ–2σ*, 1π–1π*, and 2π–2π*), so NPO analysis makes the SERS intensity much easier to understand than by conventional canonical molecular orbitals. Moreover, we analyzed the dependence of the density functional theory functional on the SERS intensity. For the Ag₂–pyrazine–Ag₂ complex, the BP86 functional overestimates the Raman intensity by about 23 times compared with coupled-cluster singles and doubles level of theory, while the CAM-B3LYP functional gives moderately accurate values. This overestimation arises from the inaccuracy of the energy derivative along the normal vibrational mode.     

20.

The features of absorption of aqueous–organic mixtures by polyurethane–poly(2-hydroxyethyl methacrylate) matrix by the data of NMR spectroscopy     

V. V. Turov  I. I. Gerashchenko  L. V. Karabanova  O. S. Kukolevska  T. V. Krupska 《Polymer Science Series A》2017,59(4):524-532

The features of hydration of the interpenetrating polymer network consisting of 83% polyurethane and 17% poly(2-hydroxyethyl methacrylate) as well as the initial polymers are studied by the method of lowtemperature NMR spectroscopy. It is shown that the two-component polymer matrix is capable of absorption of significant amounts of water in the form of clusters, with the size strongly depending on the presence of organic compounds, such as chloroform and trifluoroacetic acid. Thus, the changes in the medium composition allow one to control the state of water absorbed by the polymer in a wide range. The found effect may be used to create materials with the controlled delivery of biologically active substances whose retention by the matrix is determined to a great extent by the energy of binding of water by the polymer.     

Pulse radiolysis study of energy transfer processes in Xe–M mixtures (M=CH2F2,CHF3,CHF2Cl,CHFCl2 and CF3Cl)

The time-resolved spectroscopy measurements were used to study the kinetics of energy transfer process in the pulse radiolysis of xenon- fluoro- and chlorofluoromethanes mixtures. The main channel, at xenon pressure above 40 Torr, seems to be of third order, while at lower xenon pressures the second order process was the main one.     

Photoionization of Xe2, Xe3 and Xe4 in the 1024–1113 Å region

The mass spectra of Xe _n ⁺ clusters (n=2–13) were recorded using a supersonic beam and an ion time-of-flight mass analyser. The yield of Xe ₂ ⁺ , Xe ₃ ⁺ and Xe ₄ ⁺ cluster ions was measured with a resolution of 0.1 Å (1 meV) in the 1024–1113 Å (11.1–12.1 eV) region. Autoionizing Rydberg series of Xe₂ converging to theC ²_3/2u state of Xe ₂ ⁺ were observed in the spectrum of Xe ₂ ⁺ . The photoionization yield of Xe ₃ ⁺ and Xe ₄ ⁺ ions each displayed similar broad features that contained no fine structure corresponding to vibrational states. The broad features were assigned to autoionizing Rydberg series by analogy with the dimer ion spectrum.     

Ab initio study of electronic energy transfer in the quenching of CO*(a 3Π) by H2

Potential energy calculations for the interaction of CO(a ³Π) with H₂(X ¹Σ_g⁺) are presented, both at the MC SCF level and with the inclusion of extensive configuration interaction. In C_2v geometry, the lowest two ³B₂ surfaces exhibit a strongly avoided crossing. At the highest level of theory used, the lowest surface provides a barrier-free adiabatic pathway for energy transfer from CO(a) to H₂, the products being CO(X ¹Σ⁺) and H₂(b ³Σ_u⁺), which dissociates to two H atoms. The energy transfer occurs by a two-electron exchange mechanism.     

Metal–metal charge transfer and interfacial charge transfer mechanism for the visible light photocatalytic activity of cerium and nitrogen co-doped TiO2

Nanosized cerium and nitrogen co-doped TiO₂ (Ce–TiO_2?xN_x) was synthesized by sol gel method and characterized by powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), FESEM, Fourier transform infrared, N₂ adsorption and desorption methods, photoluminescence and ultraviolet–visible (UV–vis) DRS techniques. PXRD analysis shows the dopant decreases the crystallite sizes and slows the crystallization of the titania matrix. XPS confirm the existence of cerium ion in +3 or +4 state, and nitrogen in ?3 state in Ce–TiO_2?xN_x. The modified surface of TiO₂ provides highly active sites for the dyes at the periphery of the Ce–O–Ti interface and also inhibits Ce particles from sintering. UV–visible DRS studies show that the metal–metal charge transfer (MMCT) of Ti/Ce assembly (Ti⁴⁺/Ce³⁺ → Ti³⁺/Ce⁴⁺) is responsible for the visible light photocatalytic activity. Photoluminescence was used to determine the effect of cerium ion on the electron–hole pair separation between the two interfaces Ce–TiO_2?xN_x and Ce₂O₃. This separation increases with the increase of cerium and nitrogen ion concentrations of doped samples. The degradation kinetics of methylene blue and methyl violet dyes in the presence of sol gel TiO₂, Ce–TiO_2?xN_x and commercial Degussa P25 was determined. The higher visible light activity of Ce–TiO_2?xN_x was due to the participation of MMCT and interfacial charge transfer mechanism.     

Kinetics and mechanism of electron transfer processes in a hydrogen peroxide—trispicolinatoruthenate(II) system

Oxidation of trispicolinatoruthenate(II) complex by hydrogen peroxide leads to the formation of mer-trispicolinatoruthenium(III) in acidic or neutral solutions. Kinetics of the reaction were studied under a large excess of H₂O₂ at constant pH. The initial rate method gives a rate expression of the form: - d[\textRu(\textII)]/\textdt = k^II [\textH₂ \textO₂ ][\textRu(\textII)] - \hbox{d}[{\text{Ru}}({\text{II}})]/{\text{d}}t = k^{II} [{\text{H}}_{2} {\text{O}}_{2} ][{\text{Ru}}({\text{II}})] but the overall process examined till completion is far more complex. The rate of the reaction decreases with increasing pH to be practically completely retarded in alkaline media. The key step in the proposed reaction mechanism is the picolinato chelate ring opening followed by the substitution of the coordinated water by H₂O₂ and two-electron intramolecular ruthenium(II) oxidation. Formation of the final ruthenium(III) complex is assigned rather to the ruthenium(IV) reduction by H₂O₂ than ruthenium(II)–ruthenium(IV) comproportionation. The obtained results show the much slower rate of the trispicolinatoruthenate(II) oxidation by hydrogen peroxide or dioxygen than the mer-trispicolinatoruthenium(III) reduction by such bioreductants as cytochrome cII or some cobalt(II) reductants.     

Noble-Gas Difluoride Complexes of MOF4 (M=Mo,W); Syntheses,Structures and Bonding of NgF2 ⋅ MOF4 and XeF2 ⋅ 2MOF4 (Ng=Kr,Xe)

The NgF₂ ⋅ MOF₄ (Ng=Kr, Xe; M=Mo, W) and XeF₂ ⋅ 2MOF₄ complexes were synthesized in anhydrous HF (aHF) solvent and melts, respectively. Their single-crystal X-ray diffraction (SCXRD) structures show NgF₂ ⋅ MOF₄ and XeF₂ ⋅ 2MOF₄ have F_t−Ng−F_b- - -M arrangements, in which the NgF₂ ligands coordinate to MOF₄ through Ng−F_b- - -M bridges. The XeF₂ ligands of XeF₂ ⋅ 2MOF₄ also coordinate to F₃OM−F_b’- - -M'OF₄ moieties through Xe−F_b- - -M bridges to form F_t−Xe−F_b- - -M(OF₃)−F_b’- - -M'OF₄, where XeF₂ coordinates trans to the M=O bond and F_b’ coordinates trans to the M’=O bond. The Ng−F_t, Ng−F_b, and M- - -F_b bond lengths of NgF₂ ⋅ nMOF₄ are consistent with MOF₄ and F₃OM−F_b’- - -M'OF₄ fluoride-ion affinity trends: CrOF₄<MoOF₄<WOF₄≈F₃OMo−F_b’- - -Mo'OF₄<F₃OW−F_b’- - -W'OF₄. The [- -(F₄OMo)(μ₃-F)H- - -(μ-F)H- -]_∞ solvate was also synthesized in aHF and characterized by SCXRD. Quantum-chemical calculations show the M- - -F_b bonds of NgF₂ ⋅ MOF₄ and XeF₂ ⋅ 2MOF₄ are predominantly electrostatic, σ-hole type bonds.     

Kinetics of CO2 absorption by aqueous mixtures of N,N′-diethylethanolamine and polyamines

Aqueous solutions of N,Nʹ-diethylethanolamine (DEEA) are prospective high-capacity CO₂-capturing solvents. Their reactivity can be enhanced by promotion with absorption activators. Two polyamines were chosen as activators in this work, viz. (methylamino)propylamine (MAPA) and diethylene triamine (DETA). In a stirred cell reactor, kinetics of CO₂ absorption into aqueous DEEA/MAPA and DEEA/DETA mixtures was studied at 303 K. The molarity of DEEA was varied in the 2–2.5 M range, whereas the polyamine concentration was changed between 0.1 and 0.5 M. Pseudo–first-order rate constants were reported. Second-order rate constants for the CO₂ reactions with MAPA and DETA were determined too. DETA reacts faster than MAPA.     

Rate constants for reactions of Cl abstraction from CCl4 by CCl3CH2·CHR radicals and Br abstraction from CCl3CH2CHBrR (R=Bun, AcO, OCNC4H8, CN) by ·Re(CO)5 radicals

The rate constants for reactions of Cl abstraction from CCl₄ by CCl₃CH₂·CHR radicals and Br abstraction from CCl₃CH₂CHBrR (R=Buⁿ, AcO, OCNC₄H₈, CN) by·Re(CO)₅ radicals were determined by ESR spectroscopy using spin trapping technique. Replacement of H atoms at the C(β) atom by O or N atoms reduces the reactivity of the radicals in the reactions of Cl abstraction from CCl₄ by approximately an order of magnitude. The presence of two polar groups at the C(β) atom results in appreciable decrease in the strength of the C−Br bond in CCl₃CH₂CHBrR adducts. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 45–48, January, 2000.     

Theoretical unimolecular kinetics for CH4 + M ⇄ CH3 + H + M in eight baths, M = He, Ne, Ar, Kr, H2, N2, CO, and CH4

Ensembles of classical trajectories are used to study collisional energy transfer in highly vibrationally excited CH(4) for eight bath gases. Several simplifying assumptions for the CH(4) + M interaction potential energy surface are tested against full dimensional direct dynamics trajectory calculations for M = He, Ne, and H(2). The calculated energy transfer averages are confirmed to be sensitive to the shape of the repulsive wall of the intermolecular potential, with an exponential repulsive wall required for quantitative predictions. For the diatomic baths, the usual "separable pairwise" approximation for the interaction potential is unable to describe the orientation dependence of the interaction potential accurately, and the ambiguity in the resulting parametrizations contributes an additional uncertainty to the predicted energy transfer averages of 20-40%. On the other hand, the energy transfer averages are shown to be insensitive to the level of theory used to describe the intramolecular CH(4) potential, with a computationally efficient semiempirical tight binding potential for hydrocarbons performing equally well as an MP2 potential. The relative collisional energy transfer efficiencies of the eight bath gases are discussed and shown to be a function of temperature. The ensemble-averaged energy transferred in deactivating collisions <ΔE(d)> for each bath is used to parametrize a single-exponential-down model for collisional energy transfer in master equation calculations. The predicted decomposition rate coefficients for CH(4) agree well with available experimental rate coefficients for M = He, Ar, Kr, and CH(4). The effect of vibrational anharmonicity on the predicted rate coefficients is considered briefly.     

Kinetics and mechanism of CH3Br,CHF2Br,and C2HF4Br photolysis in the presence of dioxygen under the action of λ = 253.7 nm light

The photolysis of CH₃Br, CHF₂Br, and C₂HF₄Br mixed with oxygen under radiation emitted by a bactericidal mercury lamp (radiation intensity maximum at λ = 253.7 nm) has been investigated. Oxygen was added in order to simulate natural conditions. A photolysis mechanism has been suggested, the corresponding model calculations have been carried out, and the calculated data have been compared with experimental data. The calculated absorption cross sections are in agreement with the literature, thus proving the validity of the mechanism suggested. The ratios between the rate constants of the reactions of the photolytically generated CH₃, CHF₂, and C₂HF₄ radicals with molecular bromine and oxygen have been determined.     

The photolysis of the uranyl oxalate system—III photochemical behaviour,kinetics and mechanism in aqueous solution

The photochemical behaviour, kinetics and mechanism of the uranyl oxalate system, have been studied at 25°C and pH 4.5. The detectable ionic and molecular species after photolysis are UO₂²⁺, U(IV) and CO₂. Kinetic evidence for the participation of an uranyl oxalate (1:2) complex as the primary photo-activatable species, is reported. The suggested photolysis mechanism is in agreement with the quantitative and qualitative results of this investigation and shows similar tendencies to the mechanism suggested for the photolysis in strongly acidic (pH ≤ 1.7) solutions.     

The kinetics,catalysis and inhibition of the Baeyer—Villiger reaction in the processes of liquid-phase oxidation of organic compounds

Literary data on kinetics, catalysis and inhibition of the oxidation reaction of carbonyl compounds with peroxy acids according to the Baeyer—Villiger reaction under aerobic liquidphase oxidation conditions have been considered and discussed. The main reaction channel involves a reversible formation of α-hydroxyperoxy ester and its rearrangement to an ester or a lactone. In the case of homolytic decomposition of α-hydroxyperoxy ester no esters are formed. At all steps the formation and transformation of α-hydroxyperoxy ester are catalyzed by carboxylic acids. The possibility of formation of the second intermediate, presumably dioxirane, is shown. Catalysts of the oxidation processes such as variable-valency metal salts influence the kinetics at all steps in the Baeyer—Villiger reaction. Inhibition of ester formation in the presence of cobalt and manganese salts is associated with catalysis of homolytic decomposition of peroxy acid and α-hydroxyperoxy ester.     

Structural variability of nucleosomes detected by single-pair Förster resonance energy transfer: histone acetylation, sequence variation, and salt effects

Nucleosomes were reconstituted from 170 bp long fragments of 5S rDNA and an optimal positioning sequence, the Selex 601, with recombinant histones. In free-solution single pair F?rster resonance energy transfer (spFRET) measurements of the distance between fluorescently labeled bases in the nucleosomal DNA, the samples exhibited structural diversity. The structural heterogeneity correlated with the stability of the complexes and depended on the DNA sequence and histone acetylation. The stability of the nucleosomes was assessed via dilution-driven disruption: histone acetylation decreased nucleosome stability. The spFRET experiments used a new approach for data acquisition and analysis that we term "deliberately detuned detection" (D3). This permits the separation of subpopulations in the samples even for the low-FRET regime characteristic for the linker-DNA labeled nucleosomes. Thus, it became possible to study in more detail histone acetylation- and salt-dependent structural variations using either end- or internally labeled DNAs on the nucleosome. We found that the distance distribution of the fluorophore pairs on the linker DNA ends was much more sensitive to histone acetylation or sequence variation than that of labels on the internal part of the DNA, which was more tightly associated with the histone core. spFRET on freely diffusing nucleosomes allows us therefore to localize the influence of histone modifications and DNA sequence variations on the nucleosome structure and dynamics.     

Temperature dependence of vibrational energy transfer in liquids: VV relaxation of CO(ν = 1) by O2 in liquid Ar from 86 to 145 K

The rate constant for the energy transfer process

has been measured for CO and O₂ dilute in liquid Ar along the coexistence curve between 86 and 145 K. The results are compared to gas phase measurements of this rate constant over the same temperature range. The ratio of the rate constants in the two phases is compared to that predicted by an application of the isolated binary collision (IBC) model for energy trasnfer, which scales the energy transfer rate constants by the rate constants for binary collisions in the two phases. The theoretical predictions of the IBC model are that the liquid state energy transfer rate constant, k^ℓ, should be 30–60% greater than the gas phase energy transfer rate constant, k^g. The measured value of k^ℓ is, within the experimental error, equal to that for k^g. Possible reasons for the discrepancy are discussed.     

Solvent effects on the kinetics of solvolysis of trans-dichlorobis (N-methylethylenediamine)cobalt(III) ion in water–propan-2-ol and water–acetonitrile mixtures

First order solvolysis rates of the trans-dichlorobis (N-methylethylenediamine) cobalt(III) ion have been measured over a wide range of solvent compositions and temperatures in water–propan-2-ol and water–acetonitrile mixtures. The rate of solvolysis is faster in the former mixtures rather than the latter. Plots of log(rate constant) versus the reciprocal of the dielectric constant of the co-solvent, and also versus the Grunwald–Winstein Y-values are non-linear for both co-solvents; this non-linearity is derived from a large differential effect of solvent structure between the initial and transition states. However, extrema in the variation of enthalpy H and entropy S of activation correlate well with the extrema in physical properties of the mixtures which are related to changes in solvent structure. Linear plots of H versus S were obtained and the isokinetic temperature indicates that the reaction is entropy controlled. The application of a free-energy cycle shows that changes in solvent structure affect the pentacoordinated cobalt(III) ion in the transition state more than the hexacoordinated cobalt(III) ion in the initial state. In addition, the stabilizing influence of changes in solvent structure is greater in propan-2-ol–water mixtures than in acetonitrile–water mixtures, and the difference becomes greater as the mole fraction, x2 of the organic co-solvent increases.     

Surface-enhanced Raman scattering of M2–pyrazine–M2 (M = Cu,Ag, Au): Analysis by natural perturbation orbitals and density functional theory functional dependence

Here, we propose a new method to analyze various electronic properties of molecules based on natural perturbation orbitals (NPOs). We applied the proposed method to chemical enhancement of the surface-enhanced Raman scattering (SERS) intensity of M₂–pyrazine–M₂ (M = Cu, Ag, Au) complexes. The SERS intensity can be effectively decomposed into the contributions of four NPO pairs (1σ–1σ*, 2σ–2σ*, 1π–1π*, and 2π–2π*), so NPO analysis makes the SERS intensity much easier to understand than by conventional canonical molecular orbitals. Moreover, we analyzed the dependence of the density functional theory functional on the SERS intensity. For the Ag₂–pyrazine–Ag₂ complex, the BP86 functional overestimates the Raman intensity by about 23 times compared with coupled-cluster singles and doubles level of theory, while the CAM-B3LYP functional gives moderately accurate values. This overestimation arises from the inaccuracy of the energy derivative along the normal vibrational mode.     

The features of absorption of aqueous–organic mixtures by polyurethane–poly(2-hydroxyethyl methacrylate) matrix by the data of NMR spectroscopy

The features of hydration of the interpenetrating polymer network consisting of 83% polyurethane and 17% poly(2-hydroxyethyl methacrylate) as well as the initial polymers are studied by the method of lowtemperature NMR spectroscopy. It is shown that the two-component polymer matrix is capable of absorption of significant amounts of water in the form of clusters, with the size strongly depending on the presence of organic compounds, such as chloroform and trifluoroacetic acid. Thus, the changes in the medium composition allow one to control the state of water absorbed by the polymer in a wide range. The found effect may be used to create materials with the controlled delivery of biologically active substances whose retention by the matrix is determined to a great extent by the energy of binding of water by the polymer.