Internal dynamics of (H2O)2 and (D2O)2 dimers: II. Effective operators of physical quantities with account of inversion and exchange motions

Using the symmetry group chain methods, a model of the internal dynamics of (H₂O)₂ and (D₂O)₂ dimers that takes into account their real geometries and two nonrigid motions with the lowest energy barriers is constructed. The motions are the inversion motion (or the acceptor switching) and the exchange motion of the acceptor and donor via an intermediate trans configuration. The model rigorously describes the interactions of various motions and leads to a simple algebraic scheme of calculation of both the positions of the levels in the energy spectrum and the intensities of transitions between them. It is important that the correctness of the model is limited only by the trueness of the choice of the symmetry of the internal dynamics.     

Electronic energy transfer between dye molecules in structured solutions of H<Subscript>2</Subscript>O and D<Subscript>2</Subscript>O

The structure of H₂O+D₂O solutions was studied by correlation spectroscopy of scattered light. The correlation function and size of scatterers were both found to depend nonmonotonically on the D₂O concentration in the H₂O+D₂O mixture. Processes of transfer of electronic excitation energy between dye molecules of different types in H₂O+D₂O solutions were studied. The efficiency of these processes was found to depend extremally on the concentration of the components of the solution. A fractal distribution of the interacting dye molecules is ascertained from the experimental data. The dependence of the fractal dimensionality of the dye solutions on the D₂O concentration in the D₂O+H₂O mixture is determined.     

Electronic excitation energy transfer between dye molecules in H<Subscript>2</Subscript>O and D<Subscript>2</Subscript>O solutions in the micellar phase

Processes of electronic excitation energy transfer (EEET) in H₂O+D₂O solutions within reversed micelles with different degrees of hydration were studied. It is ascertained that the structure of solutions forms a cluster distribution of interacting molecules having a fractal dimensionality. As a result, in regions with a locally high concentration of the dye molecules, an increase in the EEET efficiency is observed. Solubilization by reversed micelles leads to destruction of the cluster structure of the water system, with the dependence of the EEET efficiency on the degree of hydration being nonmonotonic. As the degree of hydration increases, the inhomogeneities of the structure inherent in bulk water are restored.     

Melting temperature of H<Subscript>2</Subscript>, D<Subscript>2</Subscript>, N<Subscript>2</Subscript> and CH<Subscript>4</Subscript> under high pressure

The melting temperatures of H₂, D₂; N₂ and CH₄ are analysed. The computed results are in very good agreement with the experimental data in each solid. Further, the analysis indicates the presence of the melting maximum in these solids.     

III. Electron-impact dissociative ionization of C<Subscript>2</Subscript>H<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack> and C<Subscript>2</Subscript>D<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack>

The dynamics of cold atoms in conservative optical lattices obviously depends on the geometry of the lattice. But very similar lattices may lead to deeply different dynamics. In a 2D optical lattice with a square mesh, it is expected that the coupling between the degrees of freedom leads to chaotic motions. However, in some conditions, chaos remains marginal. The aim of this paper is to understand the dynamical mechanisms inhibiting the appearance of chaos in such a case. As the quantum dynamics of a system is defined as a function of its classical dynamics – e.g. quantum chaos is defined as the quantum regime of a system whose classical dynamics is chaotic – we focus here on the dynamical regimes of classical atoms inside a well. We show that when chaos is inhibited, the motions in the two directions of space are frequency locked in most of the phase space, for most of the parameters of the lattice and atoms. This synchronization, not as strict as that of a dissipative system, is nevertheless a mechanism powerful enough to explain that chaos cannot appear in such conditions.     

Kinetics of low-temperature initiation of H<Subscript>2</Subscript>/O<Subscript>2</Subscript>/H<Subscript>2</Subscript>O mixture combustion upon the excitation of molecular vibrations in H<Subscript>2</Subscript>O molecules by laser radiation

The initiation of H₂/O₂/H₂O mixture combustion when asymmetric vibrations in H₂O molecules are excited by a resonant IR laser radiation is considered. It is shown that the vibrational excitation of the molecules gives rise to new efficient channels for the formation of chemically active O and H atoms and OH radicals. As a result, the chain mechanism of combustion in the mixtures is enhanced and, as a consequence, the induction time is cut and the ignition temperature is lowered. Even at a minor radiant energy flux delivered to the gas (E_in≈2.5 J/cm²), the ignition temperature of the stoichiometric H₂/O₂ mixture containing only 5% of H₂O may become as low as 300 K.     

Description of the torsional motion in the isotopically asymmetric ionic complexes ArH<Subscript>2</Subscript>D<Superscript>+</Superscript> and ArD<Subscript>2</Subscript>H<Superscript>+</Superscript>

The internal dynamics of the isotopically asymmetric ionic complexes ArH₂D⁺ and ArD₂H⁺ is considered to be a distorted dynamics of the isotopically symmetric ArH₃⁺ complex. By using the group chain methods, a rigorous algebraic model is constructed to describe the spectrum of the asymmetric complexes with an allowance for the torsional motion of the structure of hydrogen nuclei. The model is based on the geometrical group of symmetry of internal dynamics of the isotopically symmetric ionic complex, which is used here as a noninvariant group.     

Oxidation of hydrogen sulfide and corrosion of stainless steel in gas mixtures containing H<Subscript>2</Subscript>S,O<Subscript>2</Subscript>, H<Subscript>2</Subscript>O,and CO<Subscript>2</Subscript>

The composition of volatile and solid products of oxidation of hydrogen sulfide and stainless steel in gas mixtures containing H₂S, O₂, H₂O, and CO₂ has been determined using mass spectrometry, x-ray diffraction analysis, and scanning electron microscopy. It has been shown that holding an H₂S–O₂ mixture at 301 K results in prevailing formation of elemental sulfur and iron sulfides in the form of porous hygroscopic crust on the reactor wall surface. Formation of gas-phase sulfur causes self-acceleration of the oxidation of hydrogen sulfide; the resulting water triggers corrosion of the reactor wall. Heating of the resulting sulfur-sulfide crust in O₂ medium is accompanied by formation of SO₂ and heat release at T > 508 K. After heating of the H₂S–CO₂ mixture to 615 K, H₂ and COS were found in the volatile reactants; no noticeable corrosion of the reactor wall has been detected. It has been established that addition of O₂ to the H₂S–CO₂ mixture and its heating to 673 K leads to formation of ferrous sulfates. The mechanisms of the observed processes are discussed.     

Linear and nonlinear optical properties of yttrium formate dihydrate,Y(HCOO)<Subscript>3</Subscript>·2H<Subscript>2</Subscript>O

Yttrium formate dihydrate, Y(HCOO)₃·2H₂O (point group 222), a promising new material for Raman laser frequency converters, has been reinvestigated with respect to the linear and nonlinear optical (second-harmonic generation, SHG) properties. High-precision data of refractive indices and their dispersion in the wavelength range 365–1083 nm are given, together with the three independent components of the tensor of nonlinear optical susceptibility (SHG) [d_ijk ^SHG]. A calculation of the macroscopic nonlinear optical susceptibility from the hyperpolarizabilities of the formate groups results in good agreement with the experimental values. This signals that the nonlinear optical interaction in Y(HCOO)₃·2H₂O can mainly be attributed to the formate groups. PACS 42.65.Ky; 42.70.Mp; 78.20.Ci     

Reactions C<Subscript>2</Subscript>H<Subscript>2</Subscript> + OH and C<Subscript>2</Subscript> + H<Subscript>2</Subscript>O: Ab initio study of the potential energy surfaces

The stationary points of the potential energy surfaces for the reactions C₂H₂ + OH and C₂ + H₂O are calculated using density functional theory and the coupled cluster method. The relative energies and geometric parameters of the stable intermediates and transition states are in good agreement with the results of independent studies. In most cases, the relative energies differ from the earlier published values by no more than 3 kcal/mol, whereas the rotational constants, by 1–2%. The mechanism of the reaction CCOH₂ → C₂ + H₂O is studied in detail. The possible sources of errors in the calculation methods are examined.     

II. Electron-impact dissociative excitation of C<Subscript>2</Subscript>H<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack> and C<Subscript>2</Subscript>D<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack>

Absolute cross-sections for electron-impact dissociative ionization of C₂ H₂⁺ and C₂ D₂⁺ to CH⁺, C⁺, C₂⁺ , H⁺, CH₂⁺ and C₂D⁺ fragments are determined for electron energies ranging from the corresponding threshold to 2.5 keV. Results obtained in a crossed beams experiment are analyzed to estimate the contribution of dissociative ionization to each fragment formation. The dissociative ionization cross sections are seen to decrease for more than an order of magnitude, from CH⁺ (5.37±0.10) × 10^-17 cm² over C⁺ (4.19± 0.16) × 10^-17 cm², C₂D⁺ (3.94±0.38) × 10^-17 cm², C₂⁺ (3.82±0.15) × 10^-17 cm² and H⁺ (3.37±0.21) × 10^-17 cm² to CH₂⁺ (2.66±0.14) × 10^-18 cm². Kinetic energy release distributions of fragment ions are also determined from the analysis of the product velocity distribution. Cross section values, threshold energies and kinetic energies are compared with the data available from the literature. Conforming to the scheme used in the study of the dissociative excitation of C₂H₂⁺ ( C₂ D₂⁺ )\left( {\rm C}_2 {\rm D}_2^+ \right), the cross-sections are presented in a format suitable for their implementation in plasma simulation codes.     

Quantum dynamics of the dissociation of H<Subscript>2</Subscript> on Rh(111)

The dissociative adsorption of H₂ on Rh(111) has been studied by high-dimensional quantum calculations using a coupled channel scheme. The potential energy surface was derived from ab initio total energy calculations using density functional theory together with the generalized gradient approximation to describe exchange-correlation effects. Experimentally, at high kinetic energy a step in the dissociative adsorption probability as a function of kinetic energy has been observed [M. Beutl et al., Surf. Sci. 429, 71 (1999)] which has been attributed to the opening up of a new adsorption channel. This feature in the dissociation probability is reproduced in the calculations for H₂ molecules initially in the ro-vibrational ground state but it is not related to the opening up of an additional dissociation channel. Instead, it is caused by purely dynamical effects. In addition, rotational effects in the H₂ dissociation are addressed.     

On the magnetic properties of Pr[Mn(CN)<Subscript>6</Subscript>]. 4H<Subscript>2</Subscript>O

A Prussian Blue type compound of the nominal composition Pr[Mn(CN)₆].4H₂O has been prepared. It is shown that the compound exhibits ferrimagnetism with a Curie temperature T_C=38.9 K. Observed magnetic relaxation displays a logarithmic behavior.     

Molecular Simulation of H<Subscript>2</Subscript>O,CO<Subscript>2</Subscript>, and CH<Subscript>4</Subscript> Adsorption in Coal Micropores

Based on the chemical model of coal, slit micropores with different pore sizes are established and structures are optimized in the software of materials studio. As the temperature rises, absolute adsorption capacities of H₂O are slightly affected, while absolute adsorption capacities of CO₂ and CH₄ gradually decrease. As the fugacity rises, excess adsorption curves of CO₂ experience increase-decrease-gentle three stages, while the curves of CH₄ gradually decrease. With the increase of pore size, adsorption capacities of H₂O increase, while adsorption capacities of CO₂ and CH₄ gradually decrease. H₂O firstly adsorbs on the oxygen-containing functional group, so the walls of pore are the preferential area for H₂O, while CO₂ and CH₄ choose to adsorb on–C–C–, therefore the walls are the primary area for CO₂ and CH₄. Strong potential in micropores and hydrogen bond among water molecules will promote the water adsorption, while the adsorptions of CO₂ and CH₄ are only induced by the Van der Waals interaction, but the difference between adsorption density and bulk density of CO₂ and CH₄ decides the change of excess adsorption capacity.     

A quasi-classical trajectory study of the Cl + H<Subscript>2</Subscript> (D<Subscript>2</Subscript>) reaction on a new BW3 potential energy surface

Molecular reaction dynamics of Cl + H₂ (D₂) has been studied on the latest analytical potential energy surface called BW3 using the Monte Carlo quasi-classical trajectory method. Excitation functions, differential cross sections and angular distributions of HCl and DCl products have been calculated. The excitation functions of the Cl (²P_3/2) + n-H₂ and Cl(²P_3/2) + n-D₂ reactions are also studied. The results are compared with those of quasi-classical trajectory [M. Alagia et al.: Phys. Chem. Chem. Phys. 2 (2000); F. J. Aoiz et al.: J. Phys. Chem. 100 (1996)], quantum mechanical (QM) calculations [F. J. Aoiz et al.:J. Chem. Phys. 115 (2001)] and experimental data [S. H. Lee et al.: J. Chem. Phys. 110 (1999); F. Dong et al.: J. Chem. Phys. 115 (2001)]. Discussions are given to some new results.