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Kinetic curves of the heterogeneous recombination of oxygen atoms on aluminum samples with a length of (1) 5 and (2) 25 cm; (a) the location of sample 1; (b) the glow of the positive column of a glow discharge is absent.
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Electron paramagnetic resonance is used to study the loss of oxygen atoms on the surface of aluminum in the positive column of a dc glow discharge in the air at gas pressures of 50–400 Pa and discharge currents of 5–100 mA. The probabilities of the recombination of O(3P) atoms are found to vary from 3 × 10−3 to 3 × 10−2 depending on the experimenta...
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... A relatively broad line width of that EPR signal (~250 G) is evidence that the electron of trapped oxygen atom O 1− experiences some weak interactions with neighboring reduced metal centers having Mo(V)/W(V) oxidation state with one unpaired electron. The spectrum of confined oxygen atoms observed in our work is consistent with recent similar findings [83]. The shortest distance between O1IN and W2(Mo2) center is 3.241 Å, while the distance between two O1IN centers is 4.385 Å. EPR signals disappear when a sample of compound 2 is heated under N2 atmosphere (during TG/DSC studies) which suggests its reductive nature. ...
Interactions between well-mixed fine powders of As2O3, P2O5, MoO3, WO3 and Nb2O5 at different stoichiometry in quartz ampoules under vacuum at ~1000 °C in the presence of metallic molybdenum (or niobium), over several weeks, led to shiny dichroic crystalline materials being formed in cooler parts of the reaction vessel. An addition of small quantities of metals-Mo or Nb-was made with the aim of partially reducing their highly oxidized Mo(VI), W(VI) or Nb(V) species to corresponding Mo(V), W(V) and Nb(IV) centers, in order to form mixed valence solids. Sublimed crystals of four new compounds were investigated using a variety of techniques, with prime emphasis on the X-ray analysis, followed by spectroscopy (diffusion reflectance, IR, Raman and EPR), second harmonic generation (SHG), thermal analysis under N2 and air atmosphere, and single crystals electrical conductivity studies. The results evidenced the formation of new complex solids of previously unknown compositions and structures. Three out of four compounds crystallized in non-centrosymmetric space groups and represent layered 2D polymeric puckered structures that being stacked on each other form 3D lattices. All new solids exhibit strong second-harmonic-generation (SHG effect; based on YAG 1064 nm tests with detection of 532 nm photons), and a rare
photosalient effect
when crystals physically move in the laser beam. Single crystals' electrical conductivity of the four new synthesized compounds was measured, and the results showed their semiconductor behavior. Values of band gaps of these new solids were determined using diffusion reflectance spectroscopy in the visible region. Aspects of new solids' practical usefulness are discussed.
The chemical composition of the discharge plasma in inert gases with H2O and D2 additives is investigated experimentally and theoretically for the first time. A new approach is applied to the measurement of the concentrations of plasma-produced particles. It includes the combination of the optical multispectral actinometry technique and the concept of intermediate chemically active actinometers. The scheme of the chemical processes in the plasma is elaborated. The dynamics and steady state concentrations of near 20 atomic and molecular particles are described. The experimental data on particle densities are in good agreement with the calculated values. The data on stationary particle concentrations with a variation of H2O (10⁶–10¹⁶) cm⁻³ and D2 (10¹²–10¹⁶) cm⁻³ are presented. Within these limits, the concentrations of chemically active atoms as well as 2-, 3-, and 4-atomic molecules are in the (10³–9.6 × 10¹⁵) cm⁻³ interval. The use of the new improved technique of actinometry combined with the modeling code significantly extends the capabilities of the highly sensitive spectral emission technique for the analysis of the chemical composition of the multi-component plasma.
The process of recombining oxygen atoms on the surface of an aluminum foil and thin film is investigated in the positive column of the DC glow discharge in oxygen at a gas pressure of 200 Pa, a discharge current of 50 mA, and surface temperatures of 350–530 K. It is shown that an increase in the average surface roughness leads to a decrease of the probability of the heterogeneous recombination of O(³P) atoms. The values of the apparent activation energy for the process of heterogenic recombination of oxygen atoms are calculated.
The influence of the gaseous products of heterogeneous processes, such as recombination and deactivation of active species on the physical characteristics of plasma and the rates of the processes involving electrons is considered.
