Andrej I. Panin

DIRECT CI METHOD IN RESTRICTED CONFIGURATION SPACES

A configuration interaction (CI) method in restricted CI (RCI) space obtained by imposing inequality‐type restrictions on the occupancies of groups of molecular orbitals (MOs) was studied. The direct CI approach in such space was analyzed, and some recommendations concerning practical implementation of the RCI method are given. The corresponding program has been written in FORTRAN 77 for an IBM 486 DX personal computer and has been used for electronic structure calculations on transition metal complexes using a valence MO basis with the INDO approximation.

Gaseous titanium molybdates and tungstates: Thermodynamic properties and structures

RATIONALE Titanium is a component of various construction materials, which is often used at high temperature and in an oxidizing atmosphere. Thermally stable even at high temperatures, titanium compounds may appear in the condensed phase. To predict the possibility of existence of gaseous associates formed by titanium oxides it is important to know their thermodynamic characteristics. Until the present investigation no gaseous salts of titanium were known. METHODS Measurements were performed by high-temperature Knudsen effusion mass spectrometry with a MS-1301 mass spectrometer. Vaporization was carried out using molybdenum and tungsten effusion cells containing samples of pure Au, Ti3O5 and SiO2. A theoretical study of gaseous titanium molybdates and tungstates in different spin states was performed by quantum chemical density functional theory (DFT) B3LYP and M06 methods. RESULTS On the basis of the equilibrium constants of gaseous reactions, the standard formation enthalpies of gaseous TiMoO3 (-424 ± 28 kJ/mol), TiWO3 (-400 ± 22 kJ/mol), TiMoO4 (-795 ± 29 kJ/mol), TiWO4 (-750 ± 24 kJ/mol), TiMoO5 (-1146 ± 23 kJ/mol) and TiWO5 (-1125 ± 22 kJ/mol) at 298 K were determined. Energetically favorable structures were localized and vibrational frequencies were evaluated in the harmonic approximation. Natural atomic charges, bond orders, and valence indices were calculated for all relevant structures. CONCLUSIONS The stability of gaseous species TiMoOn and TiWOn (n = 3, 4, 5) was confirmed by high-temperature mass spectrometry. A number of gas-phase reactions involving titanium-containing gaseous salts were studied. Enthalpies of reactions of gaseous TiXOn (X = Mo, W; n = 3, 4, 5) formation were evaluated theoretically and the obtained values are in agreement with the experimental ones.

Thermal stability and structures of gaseous GeB2O4 and GeMo2O7

The stability of gaseous species GeB2O4 and GeMo2O7 was confirmed by Knudsen effusion mass spectrometry. The gas-phase reactions involving B2O3, Mo2O6, MoO3, GeB2O4 and GeMo2O7 were studied. On the basis of equilibrium constants, the standard formation and atomization enthalpies of gaseous GeB2O4 (−1101 ± 18 kJ mol−1 and 3600 ± 20 kJ mol−1) and GeMo2O7 (−1449 ± 41 kJ mol−1 and 4810 ± 43 kJ mol−1) at 298 K were determined. To get structure parameters and vibrational frequencies of gaseous GeB2O4 and GeMo2O7 quantum chemical investigation of these molecules was undertaken. Formation enthalpies of gaseous GeTaO3, GeTiO3, GeVO3 and GePO2 were estimated.

Symmetry classification of electron and phonon states in TiO2 -based nanowires and nanotubes.

Procedure for deriving Wyckoff positions for nanowires (NWs) and nanotubes (NTs) from Wyckoff positions of ambient space group is described. It is proposed how to use SITESYM code available on Bilbao Crystallographic Server to calculate representations induced from orbit stabilizers for 1‐periodic groups. This procedure is demonstrated on the example of TiO2 rutile‐based NWs. General analytic expressions for Line group representations induced from irreps of their orbit stabilizers are obtained. This approach presupposes the use of the standard (crystallographic) factorization of Line groups. Computer construction of orbits and induced representations can be efficiently implemented and the corresponding computer code SITESYML, which can be considered as a certain elaboration of the existing code SITESYM is written. The application of the code is demonstrated on the example of TiO2 anatase‐based NTs with the rectangular and hexagonal morphology.

Evaluation of relative electron ionization cross-sections for some oxides and oxyacid salts

RATIONALE The total or relative cross-sections for the ionization of polyatomic molecules by electron ionization are essential data in a wide range of applications. In addition to the total ionization cross-sections, relative ionization cross-sections are sometimes also required. Accurate values of electron ionization cross-sections of high-temperature vapor species are of importance in mass spectrometric investigations. So the need for experimental ionization cross-section data for high-temperature vapor species is vital. METHODS Measurements were performed by high-temperature Knudsen effusion mass spectrometry with a MS-1301 mass spectrometer. Vaporization was carried out using molybdenum or tungsten effusion cells containing samples of pure Au and CeO2 . The vapor compositions over the CeO2 -Mo and CeO2 -W systems were determined by Knudsen effusion mass spectrometry. The method of ion currents comparison was used to measure partial pressures. The enthalpies of the reactions under study were calculated using the third law procedure. RESULTS The standard formation enthalpies of cerium molybdates and tungstates were determined from the relative ionization cross-sections of molybdenum, tungstate, cerium, and cerium salts. Cross-sections were calculated by different methods: simple adding atomic cross-sections with correction factor, using known ratios of complex ions, adding oxide cross sections. The traditional approach to determination of ionization cross-sections exploiting the values of atomic cross-sections and the additivity rules as well as literature experimental data was used. CONCLUSIONS The enthalpies of formation of gaseous cerium molybdates and tungstates were evaluated by measurements of the reaction enthalpies for several independent reactions. The best agreement was obtained with the data from the analysis of experimentally determined relative ionization cross-sections, and using ionization cross-sections of polyatomic molecules recommended by Drowart et al. The widely used additivity method, in spite of the additional corrections introduced, gives the worst convergence of the values under consideration.

Thermochemical study of gaseous salts of oxygen-containing acids: XXI. Zinc phosphate

A gas–phase reaction involving zinc phosphate was studied by the high-temperature massspectrometry method. Standard enthalpies of formation and atomization of the molecules ZnPO3(gas) were determined.

Thermodynamic study of gaseous tin molybdates by high‐temperature mass spectrometry

RATIONALE Molybdenum and tin are components of various construction materials which are often used at high temperature and in an oxidizing atmosphere. Oxides of molybdenum and tin, with their high reactivity, can, in their turn, form a number of gaseous compounds. To predict the possibility of the existence of gaseous associates formed by tin and molybdenum oxides it is important to know their thermodynamic characteristics. Until the present investigation only a few gaseous salts of tin were known. METHODS High-temperature Knudsen effusion mass spectrometry was used to determine the partial pressures of vapor species over the SnO(2) -MoO(3) system. The formation enthalpies of gaseous SnMoO(4), Sn(2) MoO(5) and SnMo(2)O(7) were derived. Measurements were performed with a MS-1301 mass spectrometer. Vaporization was carried out using a molybdenum effusion cell containing the samples under study and pure gold as the reference substance. A theoretical study of gaseous tin molybdates was performed by several quantum chemical methods: wave function based explicitly correlated F12 methods and DFT M0(6) methods. RESULTS In the temperature range of 1200-1400 K, SnO, Sn(2)O(2), SnMoO(4), Sn(2) MoO(5), SnMo(2)O(7), MoO(3), Mo(2)O(6) and Mo(3)O(9) were found to be the main vapor species over the samples studied. On the basis of the equilibrium constants of gaseous reactions, the standard formation enthalpies of gaseous SnMoO(4) (-699 ± 29 kJ/mol), Sn(2) MoO(5) (-1001 ± 38 kJ/mol) and SnMo(2)O(7) (-1456 ± 60 kJ/mol) at 298 K were determined. Energetically favorable structures were found and vibrational frequencies were evaluated in the harmonic approximation. CONCLUSIONS The stability of gaseous species, SnMoO(4), Sn(2) MoO(5) and SnMo(2)O(7), was confirmed by high-temperature mass spectrometry. A number of gas-phase reactions involving tin-containing gaseous salts were studied. The enthalpies of reactions of gaseous tin molybdates were evaluated theoretically and the obtained values are in agreement with those obtained experimentally.

Thermodynamic properties of gaseous cerium molybdates and tungstates studied by Knudsen effusion mass spectrometry

RATIONALE CeO2 -WO3 and CeO2 -MoO3 catalysts have shown excellent performance in the selective reduction of NOx by ammonia (NH3 -selective catalytic reduction) over a wide temperature range. Strong interaction between CeO2 and WO3 or MoO3 might be the dominant reason for the high activity of these mixed oxides. Studies of ceria-containing gaseous salts involve considerable experimental difficulties, since the transition of such salts to vapor requires high temperatures. To predict the possibility of the existence of gaseous associates formed by cerium and molybdenum (tungsten) oxides it is important to know their thermodynamic characteristics. Until the present investigation, gaseous cerium oxyacid salts were unknown. METHODS Knudsen effusion mass spectrometry was used to determine the partial pressures of vapor species and the equilibrium constants of gas-phase reactions, as well as the formation and atomization enthalpies of gaseous cerium molybdates and tungstates. CeO2 was evaporated from molybdenum and tungsten effusion cells containing gold metal as a pressure standard. A theoretical study of gaseous cerium gaseous molybdates and tungstates was performed by several quantum chemical methods. RESULTS In the temperature range 2050-2400 K, CeO, CeO2 , XO2 , XO3 , CeWO3 , CeXO4 , CeXO5 (X = Mo, W) and CeMo2 O7 were found to be the main vapor species over the CeO2 - Mo (W) systems. On the basis of the equilibrium constants of the gaseous reactions, the standard formation enthalpies of gaseous CeWO3 , CeXO4 , CeXO5 (X = Mo, W) and CeMo2 O7 at 298 K were determined. Energetically favorable structures of gaseous cerium salts were found and vibrational frequencies were evaluated in the harmonic approximation. CONCLUSIONS The thermal stability of gaseous cerium oxyacid salts was confirmed by high-temperature mass spectrometry. Reaction enthalpies of the gaseous cerium molybdates and tungstates from gaseous cerium, molybdenum and tungsten oxides were evaluated theoretically and the obtained values are in reasonable agreement with the experimental one.

Thermochemical study of gaseous salts of oxygen-containing acids: XXII.1 Lead salts

Reactions of gas-phase synthesis of lead phosphates and tellurates have been studied. Standard enthalpies of formation and atomization of gaseous PbPO2, PbPO3, PbP2O6, PbTeO3, and Pb2TeO4 salts have been determined.