O2 Pairs Research Articles

Characteristics of Lithium Ions and Superoxide Anions in EMI-TFSI and Dimethyl Sulfoxide.

To clarify the microscopic effects of solvents on the formation of the Li(+)-O2(–) process of a Li–O2 battery, we studied the kinetics and thermodynamics of these ions in dimethyl sulfoxide (DMSO) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI-TFSI) using classical molecular dynamics simulation. The force field for ions–solvents interactions was parametrized by force matching first-principles calculations. Despite the solvation energies of the ions are similar in both solvents, their mobility is much higher in DMSO. The free-energy profiles also confirm that the formation and decomposition rates of Li(+)-O2(–) pairs are greater in DMSO than in EMI-TFSI. Our atomistic simulations point out that the strong structuring of EMI-TFSI around the ions is responsible for these differences, and it explains why the LiO2 clusters formed in DMSO during the battery discharge are larger than those in EMI-TFSI. Understanding the origin of such properties is crucial to aid the optimization of electrolytes for Li–O2 batteries.

Characterization of a paramagnetic mononuclear nonheme iron-superoxo complex.

O2 bubbling into a THF solution of FeII(BDPP) (1) at −80 °C generates a reversible bright yellow adduct 2. Characterization by resonance Raman and Mössbauer spectroscopy provides complementary insights into the nature of 2. The former shows a resonance-enhanced vibration at 1125 cm–1, which can be assigned to the ν(O–O) of a bound superoxide, while the latter reveals the presence of a high-spin iron(III) center that is exchange-coupled to the superoxo ligand, like the FeIII–O2– pair found for the O2 adduct of 4-nitrocatechol-bound homoprotocatechuate 2,3-dioxygenase. Lastly, 2 oxidizes dihydroanthracene to anthracene, supporting the notion that FeIII–O2– species can carry out H atom abstraction from a C–H bond to initiate the 4-electron oxidation of substrates proposed for some nonheme iron enzymes.

A versatile strategy to the selective synthesis of Cu nanocrystals and the in situ conversion to CuRu nanotubes

Compared with Ag, Au, Pt and Pd, the synthesis of Cu nanocrystals that exhibit well-defined structures and surface properties has achieved limited success. Herein, we report an etching and protecting strategy to prepare Cu nanostructures with controllable shapes, crystalline nature and surface properties. In the developed strategy, the selective use of different additives is critical to the successful synthesis of the Cu nanocrystals: while NH4Cl (or hexadecyltrimethylammonium chloride (CTAC)) functions as an etchant by a Cl(-)-O2 pair that can selectively remove twinned nuclei and induce the formation of single nanocrystals with a cubic morphology, the addition of RuCl3 (or FeCl3, FeCl2) can protect the multiply twinned seeds from being etched, and leads to the formation of 5-fold twined nanowires. The controlling strategy reported herein is highlighted by its simplicity and versatility. By further increasing the reaction temperature and prolonging the reaction time, bimetallic CuRu nanotubes can be readily prepared. The applications of these well-defined nanostructures and the developed strategy in controlling other metals are currently under investigation.

Synthesis, characterization and gas transport properties of semifluorinated new aromatic polyamides

This manuscript describes the synthesis, characterization and gas transport properties of a series of poly(ether amide)s (PAs) prepared from a new diamine monomer 4,4-bis-[2′-trifluromethyl 4′-(4″-aminophenyl)phenoxy]-biphenyl on reaction with five different aromatic dicarboxylic acids. The polyamides exhibited very good film forming ability, thermal and mechanical properties (448–479°C for 10% weight loss in air, glass transition temperatures in the ranges of 252–278°C, tensile strengths up to 99MPa). PA ‘I’ having tert-butyl group showed highest permeability in barrer for PCO2=42.60, PO2=10.00, PN2=2.10, PCH4=1.80. PA ‘II’ containing hexafluroisopropylidene linkage showed highest permselectivity for O2 and N2 gas pair (PO2/PN2=7.08) whereas PA ‘IV’ showed highest permselectivity towards CO2 over CH4 (PCO2/PCH4=30.25) among the series. Attempt has been made to draw structure–property co-relationship in terms of thermal, mechanical and gas transport properties vs. the polymer repeat unit structures.

Quantum Yield and Mechanism of Singlet Oxygen Generation via UV Photoexcitation of O2–O2 and N2–O2 Encounter Complexes

The mechanism and spectral dependence of the quantum yield of singlet oxygen O(2)(a (1)Δ(g)) photogenerated by UV radiation in gaseous oxygen at elevated pressure (32-130 bar) have been experimentally investigated within the 238-285 nm spectral region overlapping the range of the Wulf bands in the absorption spectrum of oxygen. The dominant channel of singlet oxygen generation with measured quantum yield up to about 2 is attributed to the one-quantum absorption by the encounter complexes O(2)-O(2). This absorption gives rise to oxygen in the Herzberg III state O(2)(A' (3)Δ(u)), which is assumed to be responsible for singlet oxygen production in the relaxation process O(2)(A' (3)Δ(u), υ) + O(2)(X (3)Σ(g)(-)) → O(2)({a (1)Δ(g)}, {b (1)Σ(g)(+)}) + O(2)({a (1)Δ(g), υ = 0}, {b (1)Σ(g)(+), υ = 0}) with further collisional relaxation of b to a state. This mechanism is deduced from the analysis of the avoiding crossing locations on the potential energy surface of colliding O(2)-O(2) pair. The observed drop of the O(2)(a (1)Δ(g)) yield near spectral threshold for O(2) dissociation is explained by the competition between above relaxation and reaction giving rise to O(3) + O (O + O + O(2)) supposed in literature. The quantum yield of O(2)(a (1)Δ(g)) formation from encounter complex N(2)-O(2) measured at λ = 266 nm was found to be the same as that for O(2)-O(2).

Peculiarities of the Coherence of Resting-State EEG Activity in Subjects with Different Levels of Aggressiveness

By analyzing the coherence of EEG activity, we examined the spatial organization of the latter in 60 adults of both sexes characterized by dissimilar levels of different aspects of aggressiveness and hostility (diagnosed using the Buss–Durkee and Il’yin questionnaires). Recording of EEG (21 leads positioned according to the 10-20 system) was carried out in the resting state. The greatest numbers of aggressiveness level-related differences in the coherence level (values of the coherence coefficient, Kcoh) were found for oscillations of the β and γ ranges. Despite the high natural interindividual variability, the subgroup of persons with a high level of aggressiveness was characterized, in general, by somewhat smaller values of Kcoh for the δ and θ ranges (in particular in the P4–O2 pair) and greater values of Kcoh for the β1 and β2 rhythms (with an accent in the C3–P3 pair) and γ range (maximum differences in T3–T5). The subgroup of persons with a high level of hostility was distinguished by smaller Kcoh of δ, θ, and γ oscillations and greater Kcoh for the β range in pairs F8–T4 and F7–T3. Aggressive persons demonstrated greater, in general, numbers of low-coherence relations, especially in the δ and θ spectrum segments. The subgroup with domination of autoaggressiveness was characterized by several significantly lower values of Kcoh for the δ and θ ranges.

A calibration method for broad-bandwidth cavity enhanced absorption spectroscopy performed with supercontinuum radiation

An efficient calibration method has been developed for broad-bandwidth cavity enhanced absorption spectroscopy. The calibration is performed using phase shift cavity ring-down spectroscopy, which is conveniently implemented through use of an acousto-optic tunable filter (AOTF). The AOTF permits a narrowband portion of the SC spectrum to be scanned over the full high-reflectivity bandwidth of the cavity mirrors. After calibration the AOTF is switched off and broad-bandwidth CEAS can be performed with the same light source without any loss of alignment to the set-up. We demonstrate the merits of the method by probing transitions of oxygen molecules O2 and collisional pairs of oxygen molecules (O2)2 in the visible spectral range.

On the temperature dependence of the integrated intensity of the collision-induced fundamental band of O2–O2

The temperature dependence of the integrated intensity of the collision-induced fundamental band of O2–O2 pairs has been investigated. For T < 280 K, most of the intensity has been shown to arise through the long-range isotropic quadrupolar mechanism, which leads to a monotonic decrease with increasing T. Recent observations carried out at higher temperature show a small increase in the integrated intensity as T increases. Assuming that this increase in absorption is due to a short-range isotropic overlap dipole and fitting the theoretically calculated results to the experimental data, reasonable values are obtained for the magnitude and range of this dipole. The assumption is tested by calculating the corresponding spectral profiles, and it is found that these are in good agreement with the experimental measurements over the temperature range 190 K to 350 K.

Formation of HXeO in a xenon matrix: indirect evidence of production, trapping, and mobility of XeO (1(1)Sigma+) in solid Xe.

IR spectroscopy, laser induced fluorescence (LIF), and thermoluminescence (TL) measurements have been combined to monitor trapping, thermal mobility, and reactions of oxygen atoms in solid xenon. HXeO and O(3) have been used as IR active species that probe the reactions of oxygen atoms. N(2)O and H(2)O have been used as precursors for oxygen atoms by photolysis at 193 nm. Upon annealing of matrices after photolysis, ozone forms at two different temperatures: at 18-24 K from close O ...O(2) pairs and at approximately 27 K due to global mobility of oxygen atoms. HXeO forms at approximately 30 K reliably at higher temperature than ozone. Both LIF and TL show activation of oxygen atoms around 30 K. Irradiation at 240 nm after the photolysis at 193 nm depletes the oxygen atom emission at 750 nm and reduces the amount of HXeO generated in subsequent annealing. Part of the 750 nm emission can be regenerated by 266 nm and this process increases the yield of HXeO in annealing as well. Thus, we connect oxygen atoms emitting at 750 nm with annealing-induced formation of HXeO radicals. Ab initio calculations at the CCSD(T)/cc-pV5Z level show that XeO (1(1)Sigma(+)) is much more deeply bound [D(e) = 1.62 eV for XeO --> Xe+O((1)D)] than previous calculations have predicted. Taking into account the interactions with the medium in an approximate way, it is estimated that XeO (1(1)Sigma(+)) has a similar energy in solid xenon as compared with interstitially trapped O((3)P) suggesting that both possibly coexist in a low temperature solid. Taking into account the computational results and the behavior of HXeO and O(3) in annealing and irradiations, it is suggested that HXeO may be formed from singlet oxygen atoms which are trapped in a solid as XeO (1(1)Sigma(+)).

C−H···O Contacts in the Adenine···Uracil Watson−Crick and Uracil···Uracil Nucleic Acid Base Pairs: Nonempirical ab Initio Study with Inclusion of Electron Correlation Effects

Structures and stabilities of H-bonded adenine···uracil Watson−Crick (AU WC) and two uracil···uracil nucleic acid base pairs possessing C−H···O contacts (UU7, UU−C) were determined using gradient optimization with inclusion of electron correlation via the second-order Moller−Plesset (MP2) perturbational method with a 6-31G** basis set of atomic orbitals. In the AU WC pair, closest contacts occur between the N6(A) and O4(U), N1(A) and N3(U), and C2(A) and O2(U) atoms: 2.969, 2.836, and 3.568 A, respectively. For the UU7 pair the closest contact corresponds to O4···N1 and C5···O2 pairs with distances of 2.860 and 3.257 A, respectively, while in UU−C pair the closest contact was found for O4···N3 and C5···O4 heteroatoms with distances of 2.913 and 3.236 A, respectively. The nature of all intermolecular contacts in the sense of a conventional H-bonding or improper, blue-shifting H-bonding was determined on the basis of harmonic vibrational analysis, atom-in-molecules (AIM) Bader analysis of electron density,...

Theoretical Studies on Radical Spin Arrangements in the Cavity of Nanoporous Complexes

Adsorption properties in nanoporous crystals, especially Zn(BDC) (BDC=1.4-benzenedicar-boxylate) crystal, were studied theoretically. For sorbed molecules N2 and CO2 were employed and gas adsorption isotherms were obtained. In addition, O2 as S=1 magnetic radical species was also treated in order to study the magnetic properties. Magnetic interaction between O2 pairs exists and these cooperation might run in the nanoporous cavity. These results lead new approach to arrangement of organic spin radical sources and it is found that nanoporous organic-metal crystals are useful for controlling their position and orientation.

Diffusion-limited geminate recombination of O+O2 in solid xenon

The thermally activated recombination reaction O+O2→O3 is observed in solid xenon matrices and in free-standing crystals of xenon at 14–25 K on the time scale 102–105 s. The reactants are prepared as spatially separated O...O2 pairs immobilized in solid Xe at 10 K by 266 nm photodissociation of O3 precursor molecules. The temperature dependence of the ozone recovery rate yields an activation energy for diffusion of O atoms in solid xenon of 2.0±0.5 kJ/mol. This value also represents an upper limit to the potential energy barrier to the O+O2 recombination reaction itself. In dilute samples (mole fraction of ozone less than 2×10−4) more than 90% of the initial O3 is recovered during the warming cycle. Only a small fraction of O atoms (&amp;lt;20%) escape geminate recombination with the partner oxygen molecule within the pair and react with other O2 molecules or O atoms. The experimental results are interpreted within the framework of a continuous diffusion model in which the initial spatial distribution of reactants is nonrandom.

The hydrogen exchange reaction of surface deuteroxyl groups on MgO with H2

The hydrogen exchange reaction of surface OD groups on MgO with H2(—OD + H2→—OH + HD) has been investigated in order to understand the relationship between the activity and the local structure of the surface hydroxyl groups by means of i.r. spectroscopy. OD groups on the Mg atom are composed of three types exhibiting different vibrations at 2771, 2765 and 2756 cm–1. These bands correspond to the following local structures on the basis of an electrostatic model: OD—Mg5C(2771 cm–1), OD—Mg4C(2765 cm–1) and OD—Mg3C(2756 cm–1), respectively. In addition to these ‘on top’ OD groups, three different kinds of multiply bridged OD groups are also observed, at 2710, 2680 and 2600 cm–1. Among the OD groups on MgO, OD—Mg3C has the highest activity, with an activation energy of 34 ± 5 kJ mol–1. OD—Mg3C—O3C has a higher activity than OD—Mg3C—O4c, where H2 dissociates at the Mg2+—O2 pairs.

Photoperiod and light quality effects on rate of dark respiration and on photosynthetic capacity in developing seedlings of Chenopodium rubrum

Development and acclimation of energy transduction were studied in seedlings of Chenopodium rubrum L. ecotype selection 184 (50° 10′ N; 105° 35′ W) in response to photomorphogenic and photoperiodic treatments. Dark respiration and photosynthetic capacity [nmol O2 (pair of cotyledons)−1 h−1] were measured with an oxygen electrode. Changes in chloroplast ultrastructure were analyzed concomitantly. After germination, seedlings were grown at constant temperature either in darkness or in continuous light (white, red, far‐red and blue) or were subjected to diurnal cycles of light/dark or changes in light quality. Dark respiration was low in far‐red light treated seedlings. In red light treated seedlings dark respiration was high and the mean value did not depend on fluence rate or photoperiod. Blue light stimulated transitorily and modulated dark respiration in photoperiodic cycles. Photosynthetic capacity was reduced by far‐red light and increased by red light. In response to blue light photosynthetic capacity increased, with indications of a requirement for continuous energy input. Phytochrome and a separate blue light receptor seemed to be involved. In continuous red light a clear cut circadian rhythm of dark respiration was observed. Blue light had a specific effect on chloroplast structure.

Contact interaction between 129Xe and nitric oxide

The chemical shift of 129Xe in nitric oxide gas has been observed as a function of temperature and density of NO. The derivative of the frequency with respect to density gives the second virial coefficient of chemical shielding of 129Xe in nitric oxide, σ1(Xe–NO) = −0.6840 + 1.5516 × 10−3τ − 1.3142 × 10−5τ2 +7.2769 × 10−8τ3 ppm amagat−1, in which τ=T−300, and T goes from 220 to 380 K. The results are compared with the Xe in oxygen gas and the contact contribution to σ1(Xe–NO) is determined. By using Ar as the diamagnetic counterpart of an NO or O2 molecule, empirical values of the integral ℱρspine−V/kTdx3 are obtained for the Xe–NO and the Xe–O2 interaction. The empirical values of this integral are greater for the Xe–NO pair than the Xe–O2 pair. Both exhibit a slight temperature dependence.

Luminescence Sideband and Raman Spectra of Oxygen in Solid Argon

AbstractThe Raman and luminescence spectra of O2 have been studied in the O2Ar system. A simple model is used for associating the unexplained 417.6 cm−1 Raman spectrum peak for 2% O2 in solid Ar at 77 K, with O2O2 pair vibrations. For the luminescence spectrum of 0.01% O2 in Ar at 4.2 K a Greens function approach is used to describe the position and extent of the experimentally observed side band. In the one defect approach it was found that the F1 u projections have a band edge resonance for an O2 in solid Ar. However the consideration of the same projections due to an O2O2 first nearest neighbour pair in solid Ar gives typical inband contributions.

Simultaneous and Induced Electronic Transitions in Oxygen. II

A general theory of the oscillator strengths of the three bimolecular transitions, Σg+31Σg−←3Σg−3Σg−, Σg+11Δg←3Σg−3Σg−, and Σg+11Σg+←3Σg−3Σg−, in oxygen is given. The intensity of these three transitions is assumed to be derived from the allowed transitions due to mixing of the electronic terms through the intermolecular interaction. The theoretical techniques developed in Paper I of this series are used. No particular geometry for the O2···O2 pair is assumed. All electrons are included in the theory and all the interactions, allowed in the absence of intermolecular overlap, are considered. Two experimentally significant points emerge from this work. (1) Each of these three transitions should be considerably weaker than either of the two transitions Δg1 3Σg←3Σg−3Σg− and Δg1 1Δg←3Σg−3Σg− discussed in Paper I. This is because while the latter transitions can borrow from several allowed transitions, including the strongly-allowed π–π transitions, the former can borrow only from transitions involving π–σ excitation which are expected to be at higher energy and to have relatively small oscillator strengths. (2) The relative oscillator strengths of these three transitions considered here agree fairly well with experiments.

Simultaneous and Induced Electronic Transitions in Oxygen. I

A fairly general theory of the relative intensities of the transitions Δ1gΔ1g←Σ3gΣ−3g− and Σ2gΔ−1g←Σ2gΣ−2g− in oxygen is given. The theory rests on the posulate that the terms in the above transitions mix with other bimolecular terms due to the intermolecular forces. Intermolecular exchange is shown to be essential for a successful interpretation of these transitions. Calculations are done neglecting the intermolecular overlap, but including all the electrons in the theory. All the allowed interactions, in the absence of intermolecular overlap, are considered in the theory. No assumption regarding the geometry of the O2···O2 pair is made. The theory predicts that relative oscillator strengths of the above two transitions (former to latter) should be 1.20. This is in excellent agreement with the experimental results. Theoretical predictions are shown to be unaffected when the intermoledular overlap is included in the calculations. The above results are derived from the ratios of interactions and thus are independent of approximations commonly used in the evaluation of integrals.

EFFECT OF HIGH PRESSURES ON THE INFRARED AND RED ATMOSPHERIC ABSORPTION BAND SYSTEMS OF OXYGEN

Absorption intensities in the 0–0 and 1–0 bands of the infrared [Formula: see text] and the 0–0 band of the red [Formula: see text] band systems of oxygen were measured in the pure gas in the range 50 to 150 atm and in O2–N2, O2–A, and O2–He mixtures up to 3000 atm total pressure at 25 °C. The integrated absorption coefficient of each band is expressed as a power series in ρO2 and ρf, the Amagat densities of oxygen and the foreign gas, respectively. The coefficient of the linear term AρO2 is a measure of the intrinsic (magnetic dipole) absorption of the O2 molecule; it is much greater in the red than in the infrared system. The quadratic term, BρO22, gives the induced absorption in O2–O2 pairs; B is about ten times greater in the infrared than in the red system. These results explain intensity anomalies which have been observed in condensed oxygen. Induction effects in O2–N2 and O2–A pairs are much smaller than in O2–O2 pairs, and scarcely observable in O2–He pairs. The significance of these results is discussed.