Defects and characteristics of the structure and properties of aluminum oxides

Based on IR spectroscopy data, it was established that nonstoichiometry defects in the structure of aluminum oxides were components of the Wannier-Mott exciton states and included the Al-O, Al-Al, O₂, O ₂ ⁺ , O ₂ ^? , O ₂ ^2? , O₃, and O_2n isolated oscillators in the ground and electronically excited states. It was shown that their presence manifested itself by thermoemission of molecular oxygen singlet forms, excess heat capacity, and anomalous diamagnetism at elevated temperatures.     

Reaction of oxygen plasma active species with polyethylene

The composition of the polyethylene surface upon treatment in an oxygen plasma and its afterglow was studied by attenuated total reflectance IR spectroscopy and X-ray photoelectron spectroscopy. The oxidation of the surface at the lowest destruction rates was attained upon simultaneous action of excited O₂(a¹Δ_g) and ground-state oxygen molecules. However, O(³ P) atoms are involved in both the formation of oxygen-containing groups and their destruction accompanied by polymer degradation.     

Electronically excited oxygen atoms,O(21D2). A time-resolved study of the collisional quenching by the gases H2, D2, CH4, NO,NO2, N2O,and C3O2 using atomic absorption spectroscopy in the vacuum ultraviolet

Time-resolved atomic absorption spectroscopy in the vacuum ultraviolet has been employed to monitor electronically excited oxygen atoms, O(2¹D₂), following their genera-tion by the flash photolysis of ozone in the Hartley band region. We report the first values for the absolute second-order rate constants describing the removal of the excited atom on collision with the molecules H₂, D₂, CH₄, NO, NO₂, N₂O, and C₃O₂. Where possible, these data are considered within the context of restrictions arising from spin and orbital symmetry and are further discussed in tems of previously reported relative rate data derived from indirect measurements. Consideration is given to the importance of these rate con-stants in discussing processes taking place in the earth's atmosphere and in systems giving rise to chemical laser action.     

Plasma diagnostics of barrier-torch discharge in argon flow in a capillary by cross-correlation spectroscopy

The radiation kinetics of the plasma of barrier-torch disrcharge in argon flow in a capillary has been studied by cross-correlation spectroscopy. It was established that the discharge emission spectrum consists of peaks of electronically excited states of argon, bands of hydroxyl radicals, and a second positive system of nitrogen. An analysis of the spatio-temporal distributions of emission intensity for the selected spectral indicators showed that the causes of the torch are ionization waves that extend through the capillary from the electrode system with a speed of 10⁵ m/s and project up to 3–4 mm. It was established that the formation of electronically excited molecules of nitrogen N₂(C ³Π _u ) in the torch of discharge occurs mainly on the reaction between metastable electronically excited atoms of argon and molecules of nitrogen in the electronic ground state.     

Effect of diabatic correlation on the reactions of O(2 3P, 2 1D) with N2 O and CO2

Although correlation diagrams based upon the application of spin and angular momentum conservation have been shown to be a useful device in interpreting the chemistry of electronically excited atoms, experimental observations suggest that a more complete understanding of such chemical processes requires some insight into the electronic structure of the collision complex. In the absence of such information, it is possible to consider the role of diabatic correlations on the energetics of elementary processes with a view toward analyzing the behavior of the reactants along the reaction coordinate. Here, the aeronomically interesting reactions of ground state and electronically excited oxygen atoms with N₂ O and CO₂ are analyzed and the effects of low-lying molecular excited states on the reactivity of these molecules assessed.     

Cluster size effect on electron-induced luminescence

As a result of combined measurements of radiation intensity, electronically excited particles density and the density of mass-separated ions formed by a collision of electrons with CO₂, N₂O, H₂O molecules and clusters in intersecting beams it has been found that the process of ejection of electronically excited particles from clusters forms a main contribution to electron-induced luminescence in a mass-spectrum of molecular, fragmented and microcluster ions. The value of this contribution depends on the cluster sizeN. The enhancement of electron-induced luminescence by small clusters (N ? 15) has been found.     

Ir absorption spectrum of CrO2Cl2 molecules for high-lying states of the vibrational quasi-continuum

A new approach to the spectroscopy of highly excited vibrational states of polyatomic molecules has been elaborated. The molecules of CrO₂Cl₂ were prepared in states with a vibrational energy of the ground electronic term A₁ of ≈ 19000 cm⁻¹ by means of internal conversion of electronic energy from the electronic state B₁ excited by laser radiation. The spectroscopy of the vibrationally excited molecules has been carried out in the region of the ν₆ and ν₁ bands with diode and CO₂ lasers. The fwhm of the obtained spectrum was ≈ 15 cm⁻¹. The intermode interaction in CrO₂Cl₂ has been theoretically analyzed, and the calculated spectrum compared with that measured experimentally. The time evolution of the spectrum of vibrationally excited CrO₂Cl₂ molecules has been studied. The average energy transferred per one collision with unexcited CrO₂Cl₂ molecules was equal to 〈δE〉 ≈ 1200 cm⁻¹.     

Excited States of Weak Interacting Complexes of Formaldehyde and Alkali Metal Ions

The electronically excited states of formaldehyde and its complexes with alkali metal ions are investigated with the time-dependent density functional theory (TD DFT) method. Vertical transition energies for several singlet and triplet excited states, adiabatic transition energies for the first singlet and triplet excited states S₁ and T₁, the adiabatic geometries and vibrational frequencies of the ground state S₀ and the first singlet and triplet excited states S₁ and T₁ for formaldehyde and its complexes are calculated. Better agreement with the experiment than that of the CIS method is obtained for CH₂O at the TD DFT level. The nonlinear C=O?M⁺ interaction in the excited states S₁ and T₁ is weaker than the linear interaction in the ground state. In the S₀ and S₁ states, the C=O bond is elongated by cation complexation and its stretching frequency is red-shifted, but in the T₁ state the C=O bond is shortened and its frequency is blue-shifted.     

Two novel one-dimensional coordination polymers [Cu2(μ-Br)2(pcaede)2 · 2H2O] n and [Cu2(μ-Br)2(pcaede)2 · 0.5THF · 0.5H2O] n formed via self-assembly of 4-pyridine-carboxylic acid 1,2-ethanediyl ester (pcaede) with copper(I) bromide

Copper(I) bromide reacts with 4-pyridinecarboxylic acid 1,2-ethanediyl ester (pcaede) in wet Me₂CO/DMSO or THF/DMSO mixed solvents to give two novel coordination polymers [Cu₂(μ-Br)₂(pcaede)₂ · 2H₂O] _n (1) and [Cu₂(μ-Br)₂(pcaede)₂ · 0.5THF · 0.5H₂O] _n (2), respectively. X-ray diffraction analyses revealed that (1) and (2) consist of infinite one-dimensional Cu^I ion chains, in which the consecutive three Cu^I ions are bridged respectively by two Br atoms and two pcaede ligands to form a string of alternately arranged four-membered Cu₂Br₂ rings and 30-membered Cu₂(pcaede)₂ rings. In addition, while in each repeated structural unit of (1) there are water molecules as guests, respectively located in a 30-membered ring and between two 30-membered rings in adjacent Cu^I ion chains, in (2) the two kinds of guest molecules 0.5THF and 0.5H₂O lie respectively in the 30-membered ring and between the corresponding 30-membered rings in neighboring Cu^I ion chains. Structures of (1) and (2) were also characterized by i.r. spectroscopy, thermogravimetry and elemental analysis.     

Raman spectroscopic evidence of formation of p-dimethoxybenzene cation on Cu- and Ru-montmorillonites

It has been demonstrated through Raman spectroscopy that p-dimethoxybenzene (DMOB) is stably adsorbed on Cu- and Ru-montmorillonites as a cation. DMOB adsorbed is oxidized by Cu²⁺ ion in a dry atmosphere and is reduced reversibly in the presence of water vapor, the process being represented by a reversible reaction: Cu²⁺(H₂O)_n + DMOB ? Cu⁺(H₂O)_n-m + DMOB⁺ + mH₂O.     

Plasma chemistry in laser ablation processes

Based on the results of quantitative spectroscopic diagnostics (LIF in combination with time resolved emission spectroscopy) chemical dynamics in laser-produced plasmas of metallic (Ti, Al,), and graphite samples have been examined. The Nd-YAG (1064 nm, 10 ns, 100 mJ) and excimer XeCl (308 nm, 10 ns, 10 mJ) lasers were employed for ablation. The main attention was focused on the elucidation of a role of oxide and dimer formation in controlling spatio-temporal distributions of different species in the ablation plume. The results of the spatial and temporal analysis of a laser-produced plasma in air indicates the existence of diatomic oxides in the ablation plume both in the ground and excited states, which are formed from reactions between ablated metal atoms and oxygen. The efficiency of the oxidation reaction depends on the intensity and spot diameter of the ablation laser beam. The maximal concentration of TiO molecules are estimated to be of 1×10¹⁴ cm⁻³ at the time of 10 μs after the start of the ablation pulse. A comparison of spatial–temporal distributions of Ti atoms and excited TiO molecules allow us to find a correlation in their change, which proves that electronically excited Ti oxides are most probably formed from oxidation of atoms in the ground and low lying metastable states. The spectroscopic characterization of pulsed laser ablation carbon plasma has also been performed. The time–space distributions as well as the high vibrational temperature of C₂ molecules indicate that the dominant mechanism for production of C₂ is the atomic carbon recombination.     

Decorated Dawson Anion by Two Different Complex Fragments of Phenanthroline and Isonicotinic Acid: Synthesis and Properties

An unreported inorganic–organic hybrid compound [{Cu₂(phen)₂(ina)₂(H₂O)}{Cu(phen)₂}(H₂P₂W₁₈O₆₂)]·10H₂O(1) (phen = 1,10-phenanthroline, ina = isonicotinate anion) was hydrothermally synthesized and characterized with elemental analysis, IR spectroscopy, thermal analysis, luminescent spectroscopy, UV/Vis diffuse reflection spectroscopy, magnetic measurement. The crystal structure was determined with X-ray single-crystal diffraction. [Cu(phen)₂]²⁺and [Cu₂(phen)₂(ina)₂(H₂O)]²⁺ units are grafted on the Dawson anion [P₂W₁₈O₆₂]^6? via the terminal oxygen atoms of two WO₆ octahedra. In [Cu₂(phen)₂(ina)₂(H₂O)]²⁺ unit Cu²⁺ ions displays a square-pyramidal geometry, and in [Cu(phen)₂]²⁺ unit the geometry of Cu²⁺ ion is more close to triangle bipyramidal geometry including a terminal oxygen atom. Hydrogen bonds exist between the decorated Dawson anions and water molecules. The compound 1 has a narrow band gap of 2.05 eV and strong emission at 437 nm. Variable-temperature magnetic measurement of 1 shows a typical antiferromagnetic interaction in the 2–300 K temperature range.     

Time-Dependent Density Functional Theory Study on Hydrogen and Dihydrogen Bonding in Electronically Excited State of 2-Pyridone–Borane–Trimethylamine Cluster

In this work, the intermolecular dihydrogen and hydrogen bonding interactions in electronically excited states of a 2-pyridone (2PY)–borane–trimethylamine (BTMA) cluster have been theoretically studied using time-dependent density functional theory method. Our computational results show that the S₁ state of 2PY–BTMA cluster is a locally excited state, in which only 2PY moiety is electronically excited. The theoretical infrared (IR) spectra of the 2PY–BTMA cluster demonstrate that the N–H stretching vibrational mode is slightly blue-shifted upon the electronic excitation. Moreover, the computed IR spectrum of the 2PY–BTMA cluster exhibits no carbonyl character due to the extension of the C=O bond length in the S₁ state. However, the N–H bond is shortened slightly upon photoexcitation. At the same time, the H···H and H···O distances are obviously lengthened in the S₁ sate by comparison with those in ground state. In addition, the electron density of the carbonyl oxygen is diminished due to the electronic excitation. Consequently, the proton acceptor ability of carbonyl oxygen is decreased in the electronic excited state. As a result, it is demonstrated that the intermolecular dihydrogen and hydrogen bonds are significantly weakened in the electronically excited state.     

氧分子在Cu2O(111)表面吸附与解离的理论研究

本文采用密度泛函方法结合周期性平板模型,研究了氧原子和氧分子在完整和存在缺陷的Cu₂O(111)表面的吸附。计算结果表明氧原子倾向于吸附在配位饱和的Cu_CSA位,而对于氧分子,则强烈倾向于吸附在配位不饱和的Cu_CUS位。氧分子在含有氧空位的缺陷表面的优势吸附位为平行吸附于空位上方的桥位。过渡态的计算表明氧分子在缺陷表面的解离是一个活化能很小的放热过程。     

Vibrational nonequilibrium and electronic excitation in the reaction of hydrogen with oxygen behind a shock wave

A theoretical analysis of ignition and combustion processes in a hydrogen-oxygen mixture behind a shock wave is presented (1000 K ≤ T ≤ 2500 K; 2.0 atm ≥ P ≥ 0.3 atm). The experiments performed using stoichiometric mixtures with the detection of OH (²Σ⁺) and rich mixtures with the detection of OH (²Π) were interpreted in terms of a general kinetic approach. In this case, the apparent rate constant of the chain branching reaction H + O₂ → O + OH was the only adjustable parameter. It was found that this rate constant increased with decreasing hydrogen content and exceeded equilibrium values. In this context, the mechanism of chain branching, which occurs through the formation of the vibrationally excited radical HO₂(v), and the role of secondary vibrationally nonequilibrium O₂ and O₂(¹Δ) molecules and the reaction H + O₂(¹Δ) → O + OH are discussed. New mechanisms of the formation and quenching of electronically excited OH(²Σ⁺) radicals, O(¹ D) atoms, and O₂(¹Δ) molecules are considered. The results of a nonempirical (ab initio) analysis of molecular systems and the corresponding estimations of reaction rate constants were widely used.     

A study of copper oxide catalysts used in the methylchorosilane reaction and determination of the fate of oxygen

The relative effectiveness of CuO and Cu₂O were compared as catalysts for the methylchlorosilane (MCS) reaction. MCS reactions catalyzed by CuO had higher rates (0.15 g/g Si-h) than MCS reactions catalyzed by Cu₂O (0.08) AND higher selectivities (4–5 points in % Di higherfor CuO). A synthetic method was found for making ¹⁷O-labeledCu₂O based on reaction of CuCl with excess NaCl and >2equivalents of Na¹⁷OH. The Na¹⁷OH was made from¹⁷O-enriched water and Na. The % enrichment of theCu₂O was determined by reduction of the Cu₂O with H₂ to form Cu and water and then subsequent reaction of the water product with Me₂SiCl₂ to make cyclo-octamethyltetrasiloxane (D₄). The ¹⁷O enrichment of the D₄ wasthen determined by mass spectroscopy. Thus Cu₂O was made with27% ¹⁷O ±5%. The labeled Cu₂Owas used as the catalyst in the MCS lab reactor. A 14% enrichmentin ¹⁷O in D₄ and dichlorotetramethyldisiloxane(M^ClM^Cl) was found vs. the controlexperiment with natural abundance oxygen Cu₂O. Thus all of the oxygen from the copper oxide catalyst ends up as siloxane; 50% of the oxygen in the product siloxane comes from other sources. Copper oxide catalyst was used in the presence of the phosphorus promoters Cu₃P and PEt₃. In both phosphorus promoter experiments, the resultant MCS lab beds were subjected toacetonitrile extraction and then NMR analysis of the extracts. Theseextracts showed that phosphorus-containing species were present and thatwhen Cu₃P was the promoter, phosphorus products containing¹⁷O were present. Thus for Cu₃P, some of thephosphorus reacts with the ¹⁷O from the Cu₂O catalyst.     

An ab initio SCF and CI study of ketene imine

The electronic structures of the ground and excited states of ketene imine (_H^HCCNH) have been studied by ab initio SCF and CI calculations. The nucleophilic nature of the β carbon with respect to nitrogen has been discussed using calculated electrostatic potentials and by calculated energy differences between the parent and protonated species. The electronically excited ¹A″ and ³A″ states are found to be almost degenerate.     

Influence of silicon coordination surrounding on the chemical structure of oxides

A comparative analysis of structural features of SiO₂ polymorphic modifications was made by Raman, and high-resolution electronic spectroscopy. It was found that the presence of isolated Si-O, Si-Si, and O-O oscillators in the ground and electronically excited states is a characteristic feature of all the structures involving silicon atoms in oxygen tetrahedral coordination surrounding. It was shown that the increase in the silicon coordination number to six (stishovite) leads to a decrease in the extent of formation of electronically excited states due to removal of barriers to the relaxation of excitation energies. This conclusion is confirmed by the low-frequency shift of the fundamental absorption and by the disappearance of the high-frequency anomaly (Si-O) and characteristic lines of Si-Si oscillators.     

Electronically excited oxygen states in exoemission and heterogeneous catalytic oxidation reactions

The role played by electronically excited oxygen in exoemission and heterogeneous catalysis is considered. The results obtained in a study of thermally stimulated exoemission from the surface of Al₂O₃ and SiO₂ are compared with data of temperature-programmed desorption of singlet oxygen O₂(¹Δ_g) from the surface of Al₂O₃ and HZSM-5 zeolites with different SiO₂/Al₂O₃ ratios. The role played by electronically excited oxygen states in heterogeneous catalysis is discussed on the basis of our own and literature data. Thermally stimulated exoemission after the action of an electron flow is considered taking into account electron-stimulated desorption and the available data on electron bombardment in catalysis.     

Radiationless decay of excited states of tetrahydrocannabinol through the S 1–S 0 (conical) intersection

The ground and electronically excited singlet states of tetrahydrocannabinol have been studied theoretically using density functional and time-dependent density functional methods. The vertical excitation energies, the equilibrium geometries as well as the adiabatic excitation energies have been determined. Opening of the six-membered ring between the oxygen and carbon atoms has been considered as photochemical reaction path. This mechanism leads to a typical excited-state intramolecular hydrogen-transfer process and produces low-lying S ₀–S ₁ intersection (possible conical intersection, CI) which provides a channel for effective radiationless deactivation of the electronically excited state.