Observation of rotational resonances of ortho and para spin isomers of the H<Subscript>2</Subscript>O molecule in hexagonal ice using four-photon laser spectroscopy

Rotational resonances of ortho and para spin isomers of the H₂O molecule are observed in hexagonal ice using four-photon spectroscopy of coherent light scattering. It is experimentally shown that the resonant contribution to the four-photon scattering signal from para H₂O spin isomers in ice is about half as large as that in the liquid phase.     

Temperature evolution of the relative concentration of the H2O ortho/para spin isomers in water studied by four-photon laser spectroscopy

The four-photon laser spectroscopy of molecular motions [1] of distilled water in the terahertz and subterahertz spectral ranges is employed to observe resonant lines related to the rotational transitions of ortho and para nuclear spin isomers of the H₂O molecule. It is demonstrated that the intensity ratio of the lines of the H₂O ortho/para spin isomers in several water samples decreases by a factor of 2.0–2.5 in comparison with the gas-phase ratio. A violation of the equilibrium ortho/para ratio upon the condensation of vapor is interpreted as a manifestation of the spin selectivity in the formation of the H-bonded complexes of the H₂O para isomers. The nonequilibrium ortho/para ratio characterizes water at room temperature as an unstable liquid with respect to the spin temperature.     

On the possibility of enrichment of H2O nuclear spin isomers by adsorption

Experimental data on the enrichment of H₂O nuclear spin isomers by means of adsorption, as suggested in several works by other authors, are reported. We were unable to observe any enrichment of isomers. The conclusion was drawn that the adsorption characteristics of water ortho and para isomers were insignificantly different. An analysis of the relaxation of H₂O spin isomers induced by the intramolecular mixing of the molecular ortho and para spin states and caused by collisions with paramagnetic oxygen molecules was performed.     

H2O and D2O spin-isomers as a mediator of the electron transfer in the reaction center of purple bacteria

The dynamics of charge separation states has been numerically simulated in order to calculate the polarization (in the third order of the perturbation theory) and its evolution in a pulsed optical field. Time evolution of the rotational states of the ortho-D₂O isomer with a nonzero magnetic momentum and mixed ortho/para-D₂O states have been calculated on the basis of the Liouville equation for the density matrix and the Redfield relaxation model for molecular aggregates. Frequencies similar to the known experimental frequencies of the modulation of the kinetics (electron transfer) of the reaction centers special pair in purple bacteria are selected from the set of calculated rotational-resonance frequencies. This semiquantitative coincidence of frequencies (within the experimental error) confirms the previously stated hypothesis, according to which the ortho-H₂O (D₂O) spin isomer can play a role of mediator during electron transfer in the reaction centers of purple bacteria.     

Conversion of ortho-para H2O isomers in water and a jump in erythrocyte fluidity through a microcapillary at a temperature of 36.6±0.3°C

A mechanism is proposed for the previously observed [1] jump in erythrocyte fluidity through a microcapillary 1.3 μm in diameter at a temperature of 36.6±0.3°C. Our interpretation is based on the experimental evidence both for existence of ortho and para H₂O isomers in water and on spin-selective interaction of proteins with para H₂O isomers as hydration shells of biomolecules are being formed [2]. It is important that the formation of hydration shells of proteins and DNA in aqueous solutions is accompanied by an increase in the Brillouin shift to 0.4 cm⁻1 (≃0.25 cm⁻¹ in water), which points to the formation of icelike structures. We believe that the coincidence of the translational energy kT of the Brownian motion and the energy of the rotational quanta for the 3₁₃–2₀₂ transition of para H₂O isomers at the temperature 36.6°C increases the probability for excitation of para H₂O isomers in collisions. Collisions mix quantum states of closely spaced levels in para H₂O (3₁₃, 285.2 cm⁻¹) and ortho H₂O (3₃₀, 285.4 cm⁻¹) and induce conversion of para isomers to ortho H₂O. It is assumed that this conversion in the icelike hydration shell of hemoglobin (Hb) is accelerated under the catalyzing effect of oxygen and iron present in Hb and triggers a chain reaction: release of ortho H₂O isomers through the erythrocyte membrane→compaction of Hb molecules and increase in concentration of catalysts→acceleration of conversion→structural gel-sol transition. It is the sequence of these processes that provides a jump in fluidity of erythrocytes through a microcapillary and the anomalous increase in fluidity of the aqueous solution of hemoglobin by almost an order of magnitude at temperatures close to 36.6°C and an increase in the solution concentration by a factor of 1.7.     

Coincidence of rotational energy of H<Subscript>2</Subscript>O ortho-para molecules and translation energy near specific temperatures in water and ice

A hypothesis of the quantum nature of the specific temperatures T _s of water and ice, whose values is not random, was formulated. It was found that the quantum energy hΩ _mn of closely located rotational transitions in the ortho and para spin isomers of H₂O molecules coincides with the translation energy kT near the well-known specific temperatures T _s in ice and water. On the basis of this fact it was suggested that ortho-para conversion occurs at temperatures close to T _s upon inelastic collisions and resonance energy exchange kT _s ↔ hΩ _mn in the rotation-translation-rotation (RTR) processes. Such conversion can induce rearrangement of the H-bond set structure and repacking of H₂O molecules. The coincidence kT _s ≈ hΩ _mn was checked for ice and water at 12 known T _s, as well as for heavy water D₂O near T _s = 11.2°C (maximum density) and −140°C (glassy transition). The previously observe strong deformation of the OH Raman band near T _s = 4, 19, 36, and 76°C (maximum density, maximum surface tension, minimum heat capacity, and maximum speed of sound, respectively) was interpreted as a manifestation of the water structure rearrangement induced by H₂O ortho-para conversion.     

Threshold effect of microwave power on ferromagnetic resonance in K<Subscript>0.4</Subscript>[Cr(CN)<Subscript>6</Subscript>][Mn(S)-pn](S)-pnH<Subscript>0.6</Subscript> single crystals

A stepwise change in the ferromagnetic resonance spectrum in a K_0.4[Cr(CN)₆][Mn(S)-pn](S)-pnH_0.6 chiral magnet has been observed in a critical microwave magnetic field of 1.8 Oe. The threshold changes in the ferromagnetic resonance spectra are caused by Suhl instability leading to the generation of defects of the magnetic structure, chiral spin solitons. The threshold effect is not observed in the same microwave range in similar chiral crystals [Cr(CN)₆][Mn(S)-pnH(H₂O)](H₂O) with a stronger Heisenberg exchange interaction.     

Effect of gasification reactions on biomass char conversion under pulverized fuel combustion conditions

The effect of gasification reactions on biomass char conversion under pulverized fuel combustion conditions was studied by single particle experiments and modelling. Experiments of pine and beech wood char conversion were carried out in a single particle combustor under conditions of 1473-1723 K, 0.0-10.5% O₂, and 25-42% H₂O. A comprehensive progressive char conversion model, including heterogeneous reactions (char oxidation and char gasification with CO₂ and H₂O), homogeneous reactions (CO oxidation, water-gas shift reaction, and H₂ oxidation) in the particle boundary layer, particle shrinkage, and external and internal heat and mass transfer, was developed. The modelling results are in good agreement with both experimental char conversion time and particle size evolution in the presence of oxygen, while larger deviations are found for the gasification experiments. The modelling results show that the char oxidation is limited by mass transfer, while the char gasification is controlled by both mass transfer and gasification kinetics at the investigated conditions. A sensitivity analysis shows that the CO oxidation in the boundary layer and the gasification kinetics influence significantly the char conversion time, while the water-gas shift reaction and H₂ oxidation have only a small effect. Analysis of the sensitive parameters on the char conversion process under a typical pulverized biomass combustion condition (4% O₂, 13% CO₂, 13% H₂O), shows that the char gasification reactions contribute significantly to char conversion, especially for millimeter-sized biomass char particles at high temperatures.     

Coherent laser spectroscopy of RF resonances in liquid

Four-photon polarization spectra of double distilled water subjected to a special treatment in a cavitation chamber and 20% aqueous solution of hydrogen peroxide were recorded in the range ±8 cm⁻¹. All recorded spectra contain narrow (< 0.3 cm⁻¹) resonances corresponding to the frequencies of the rotational spectrum of ortho and para spin isomers of the H₂O molecule. Numerical simulation of the spectra obtained made it possible to quantitatively estimate the contribution of the rotational spectrum to the coherent scattering signal. It was found that the contribution of the para spin isomer of the H₂O molecule to the rotational line spectrum decreases in an aqueous solution of the α-chymotrypsin protein. Apparently, this decrease indicates the selectivity of interaction of biopolymer molecules with different spin isomers.     

Positronium interactions with Cu(II) Ions in water

Summary Positronium reactions with Cu(II) ions in aqueous solution were investigated by measuring the concentration dependence of lifetime spectra and of 1D-ACAR curves for the following Cu (II) complexes: [Cu(H₂O)₆[²⁺, [Cu(NH₃)₄ (H₂O)₂]²⁺ and [Cu(EDTA)(H₂O)]²⁻. The combined analysis of lifetime and ACAR data shows that Cu(II) ions:a) reduce the formation of positronium (inhibition effect),b) promote both ortho ⇌ para conversion and redox reactions. It was also found that inhibition and reaction rate constants are affected by the ligand type.     

Generation of MoS<Subscript>2</Subscript> quantum dots by laser ablation of MoS<Subscript>2</Subscript> particles in suspension and their photocatalytic activity for H<Subscript>2</Subscript> generation

MoS₂ quantum dots (QDs) have been obtained in colloidal suspensions by 532 nm laser ablation (7 ns fwhp/pulse, 50 mJ/pulse) of commercial MoS₂ particles in acetonitrile. High-resolution transmission electron microscopy images show a lateral size distribution from 5 to 20 nm, but a more homogeneous particle size of 20 nm can be obtained by silica gel chromatography purification in acetonitrile. MoS₂ QDs obtained by laser ablation are constituted by 3–6 MoS₂ layers (1.8–4 nm thickness) and exhibit photoluminescence whose λ_PL varies from 430 to 530 nm depending on the excitation wavelength. As predicted by theory, the confinement effect and the larger periphery in MoS₂ QDs increasing the bandgap and having catalytically active edges are reflected in an enhancement of the photocatalytic activity for H₂ generation upon UV–Vis irradiation using CH₃OH as sacrificial electron donor due to the increase in the reduction potential of conduction band electrons and the electron transfer kinetics.     

Anomalous absorption in H<Subscript>2</Subscript>CN and CH<Subscript>2</Subscript>CN molecules

Structures of H₂CN and CH₂CN molecules are similar to that of H₂CO molecule. The H₂CO has shown anomalous absorption for its transition 1₁₁–1₁₀ at 4.8 GHz in a number of cool molecular clouds. Though the molecules H₂CN and CH₂CN have been identified in TMC-1 and Sgr B2 through some transitions in ortho as well as in para species, here we have investigated the condition under which transitions 1₁₁–1₁₀ and 2₁₂–2₁₁ of these molecules may show anomalous absorption. For the present investigation, we have calculated energy levels and radiative transition probabilities. However, we have used scaled values for collisional rate coefficients. We found that relative values of collisional rate coefficients can produce the required anom-alous absorption in 1₁₁–1₁₀ and 2₁₂–2₁₁ transitions in the molecules.      

Potential Energy Surface for Oxidation of Indenyl C<Subscript>9</Subscript>H<Subscript>7</Subscript>

Ab initio calculations were performed to obtain local energy extrema, including an effect of reagents, intermediates, and reaction products on the potential energy surface for the C₉H₇+O₂ reaction, playing a significant role in oxidation of polycyclic aromatic hydrocarbons at combustion conditions. The final products, determined as a result of the calculations are styrenyl radical C₈H₇+CO₂, ortho-vinyl phenyl radical C₈H₇+CO₂ and 1-H-inden-1-one C₉H₆O+OH, which is predicted to be the prevailing reaction product.     

Kinetics of electron tunneling transfer in KH<Subscript>2</Subscript>PO<Subscript>4</Subscript> and NH<Subscript>4</Subscript>H<Subscript>2</Subscript>PO<Subscript>4</Subscript> crystals with hydrogen bonds

A model of electron transfer by tunneling between trapped electron and hole centers in crystals with hydrogen bonds under the conditions of thermostimulated mobility of one carrier type in the recombination process has been developed. The proposed model describes all features in the kinetics of induced optical density relaxation observed in nonlinear optical crystals of KH₂PO₄ (KDP) and NH₄H₂PO₄ (ADP) on a wide temporal scale (10⁻⁸–10 s) under pulsed irradiation. The results of model calculations have been compared with experimental data on the photoinduced transient optical absorption (TOA) in KDP and ADP crystals in the visible and UV ranges. The nature of the radiation-induced defects, which account for the TOA, and the dependence of the TOA decay kinetics on the temperature, excitation power, and other experimental conditions have been considered.     

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.     

Magnetic structure of the quasi-one-dimensional frustrated antiferromagnet LiCu<Subscript>2</Subscript>O<Subscript>2</Subscript> with Spin <Emphasis Type="Italic">S</Emphasis> = 1/2

The magnetic properties of LiCu₂O₂ single-crystal samples without twinning are investigated using electron spin resonance and nuclear magnetic resonance spectroscopy. The experimental results obtained are described in terms of the model of a planar spiral antiferromagnet for the orientation of the magnetic field H ‖ b or H ‖ c and the model of a collinear spin-modulated antiferromagnet for the orientation of the static magnetic field H ‖ a.     

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.     

Nuclear spin conversion in CH F induced by an alternating electric field

The nuclear spin conversion in CH₃F molecules subjected to an alternating electric field was investigated experimentally. The conversion rate was found to be almost unaffected by low electric fields ( V/cm) but sharply increased tenfold when the electric field amplitude exceeds the values ( V/cm) sufficiently high to produce crossings of the ortho and para states of the molecule. A theoretical model for the molecular conversion in alternating electric field was developed. The results of the experiment were found to be in a good agreement with the theory. Received 23 July 1999 and Received in final form 7 September 1999     

Magnetic properties of the tetranitrosyl-iron complex Fe<Subscript>2</Subscript>(SC<Subscript>3</Subscript>H<Subscript>5</Subscript>N<Subscript>2</Subscript>)<Subscript>2</Subscript>(NO)<Subscript>4</Subscript>

The magnetic properties of the binuclear nitrosyl-iron complexes Fe₂(SC₃H₅N₂)₂(NO)₄ are investigated. It is demonstrated that several types of particles, such as dimers with a pair of spins 1/2, dimers with a pair of spins 5/2, and paramagnetic particles with spin 3/2, make a contribution to the magnetic properties of the complexes. A decrease in the temperature below 25 K leads to a change in the shape of the EPR spectra corresponding to these dimers, so that Lorentzian lines (homogeneous broadening) transform into Gaussian lines (inhomogeneous broadening). This is accompanied by a stepwise change in the EPR line width and g factors. The change in the line shape indicates that complexes become asymmetric at low temperatures, possibly, due to the decrease in the spin exchange frequency below the frequency of the microwave field of the spectrometer.     

On the Measurement of the Stiffness of Spin Waves in the Fe<Subscript>0.75</Subscript>Co<Subscript>0.25</Subscript>Si Helimagnet by the Small-Angle Neutron Scattering Method

The stiffness of spin waves in the Fe_0.75Co_0.25Si helimagnet with the Dzyaloshinskii–Moriya interaction in a state fully magnetized by an external field has been measured by the small-angle neutron scattering method. It has been shown that the dispersion of magnons in this state is anisotropic because the neutron scattering pattern consists of two circles for neutrons with obtaining and losing the magnon energy, respectively. The centers of the circles are shifted by the momentum transfer oriented along the applied magnetic field H and equal to the wave vector of the spiral ±k_s measured in inverse nanometers. The radius of the circles is directly related to the stiffness of spin waves and depends on the magnitude of the magnetic field. It has been shown that the stiffness of spin waves A for the helimagnet is equal to 46.0 meV Ų at T = 0 K and decreases weakly (by 20%) with increasing temperature up to the critical value T_c = 38 K.