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.     

Spectroscopic evidence for the effect of the ortho H<Subscript>2</Subscript>O spin on the electron transfer in photosynthesis

A spin mechanism for electron transfer control in the reaction center of purple bacteria in photosynthesis is proposed. Rotation and conversion of the ortho/para spin isomers of two H₂O molecules located near the special pair of the reaction center are treated as the sources of the coherent modulations of transient kinetics. Modulation of the collective wave function of the reaction center electrons by the total proton spin of ortho H₂O is a key feature allowing the molecule to play the role of a gate controlling the electron transfer. The iron atom in the reaction center with the gradient magnetic field is treated as a catalyst removing the strict forbiddenness of H₂O ortho/para conversion. It is shown that the modulation of the reaction center stimulated emission kinetics observed in the field of femtosecond pulses coincides with the rotational transitions of ortho/para H₂O. Influence of the effect of the electric field (Stark effect) on the level displacement and ortho/para conversion rate is discussed.     

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.     

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.     

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.     

Probing the isomer,fluorination and bond effects in C<Subscript>3</Subscript>H<Subscript>6</Subscript>, cyclo-C<Subscript>3</Subscript>H<Subscript>6</Subscript> and C<Subscript>3</Subscript>F<Subscript>6</Subscript> molecules using electron impact

We have carried out experimental and theoretical studies on electron scattering from the C₃H₆ isomers and C₃F₆ molecules and we report on total, differential as well as theoretical integral elastic cross-sections for these molecules. Vibrational excitation functions are also presented for the typical vibrational peaks in C₃H₆ and cyclo-C₃H₆ for the angle of 90^○, impact energy range of 1–16 eV and loss energies of 0.12 eV and 0.13 eV, respectively. In the cross-sections, clear differences in peak positions and magnitudes between the C₃H₆ isomers can be viewed as the isomer effect. The same is observed between C₃H₆ and C₃F₆ in a clear manifestation of the fluorination effect. The resemblance of the π^* shape resonance in the cross-sections, observed at about 2.2 eV for C₃H₆ and 3.5 eV for C₃F₆, to those in C₂H₄ and C₂F₄ clearly points to the effect of the double bond in the molecular structures for these molecules. Theoretical analysis is performed to provide rationales for the scattering dynamics.     

Four-photon laser spectroscopy of translational vibrations of a proton in water and hexagonal ice

For the first time, translational vibrations of a proton in H₂O, D₂O, HDO, and hexagonal ice were found in the Rayleigh line wing using four-photon polarization spectroscopy.     

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.     

Elastic properties of D<Subscript>2</Subscript>O ices in solid-state amorphization and transformations between amorphous phases

Nonequilibrium phase transformations in D₂O ices, including the solid-state amorphization of ice 1h (1h-hda) and the heating-induced transition cascade hda-lda-1c-1h from high-density amorphous (hda) ice to low-density amorphous (lda) ice followed by crystallization in cubic ice 1c and phase transition to ordinary hexagonal ice 1h, were studied using an ultrasonic technique. It has been shown that, as in H₂O ice, the softening of a crystal lattice or an amorphous network precedes nonequilibrium transformations. However, noticeable isotopic differences in the behavior of the elastic properties of H₂O and D₂O, in particular, their 1h and hda modifications, call for a more detailed study of the structural features of these H₂O and D₂O phases.     

Four-photon laser spectroscopy of low-frequency rotational resonances of H<Subscript>2</Subscript>O molecules in the liquid phase

A clearly pronounced structure of the Rayleigh wing consisting of a great number of components is measured in the range 0–100 cm^?1 using four-photon polarization spectroscopy. The features observed are compared with the calculated IR spectra of H₂O molecules in the gas phase taken from the HITRAN database. A good correlation between the frequency positions of the observed and calculated lines points to the possibility of hindered rotation of water molecules in liquid.     

Spin dynamics and four-photon mixing in InSb

The spin flip Raman interaction can be used to excite coherent spin precession in semiconductors. Resonant, four-photon mixing is shown to be equivalent to Raman scattering from this coherent state. Studies of the four-photon intensity give information concerning spin dynamics (T₁ and T₂) in n-InSb.     

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.     

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.     

Detection of the structure of the wing of the Rayleigh line in ice, water, and heavy water using four-photon polarization spectroscopy

The spectral structure of the wing of the Rayleigh line in ice, ordinary water (H₂O), and heavy water (D₂O) is recorded in the frequency range 0–50 cm⁻¹ by means of four-photon polarization spectroscopy. It is shown that this structure can be explained by the collective rotational motion of molecules in cells determined by the structure of hexagonal ice. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 1, 12–14 (10 January 1999)     

The temperature evolution of the magnetic correlations in pure and diluted spin ice Ho2−xYxTi2O7

Diffuse polarized neutron scattering studies have been carried out on single crystals of pyrochlore spin ice Ho_2−xY_xTi₂O₇ (x=0, 0.3, and 1) to investigate the effects of doping and anisotropy on spin correlations in the system. The crystals were aligned with the (1 −1 0) orientation coincident with the direction of neutron polarization. For all the samples studied the spin flip (SF) diffuse scattering (i.e. the in-plane component) reveals that the spin correlations can be described using a nearest-neighbour spin ice model (NNSM) at higher temperatures (T=3.6 K) and a dipolar spin ice model (DSM) as the temperature is reduced (T=30 mK). In the non-spin flip (NSF) channel (i.e. the out-of-plane component), the signature of strong antiferromagnetic correlations is observed for all the samples at the same temperature as the dipolar spin ice behaviour appears in the SF channel. Our studies show that the non-magnetic dopant Y does not significantly alter SF or NSF scattering for the spin ice state, even when Y doping is as high as 50%. In this paper, we focus on the experimental results of the highly doped spin ice HoYTi₂O₇ and compare our results with pure spin ice Ho₂Ti₂O₇. The crossover from a dipolar to a nearest-neighbour spin ice behaviour and the doping insensitivity in spin ices are briefly discussed.     

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.     

Synthesis of CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles with tunable magnetism by the modified hydrothermal method

Cobalt ferrite (CoFe₂O₄) nanoparticles were synthesized by using the hydrothermal route with the addition of trisodium citrate dihydrate (Na₃CA·2H₂O). The formation of CoFe₂O₄ nanoparticles with size ranging from 13 to 19 nm was confirmed by X-ray diffraction, energy dispersive X-ray analysis, and Fourier transform infrared spectroscopy; the clear-cut sharp of the nanoparticles was observed by transmission electron microscopy. By these characterization methods, the evolution of lattice constant and morphologies of the nanoparticles with the addition of Na₃CA·2H₂O is observed. Furthermore, the magnetic hysteresis loops measured at room temperature indicate that the magnetic properties of the products also show clear relationship with the masses of Na₃CA·2H₂O. For example, coercivity and high-field paramagnetic susceptibility increase with the increasing masses of Na₃CA·2H₂O, whereas the saturation magnetization and the effective magnetic anisotropy constant have the maximum values as the mass of Na₃CA·2H₂O is 1 g. This change of magnetic properties is related with the expanded lattice and the varied size and shape because of the addition of Na₃CA·2H₂O.     

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.     

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.     

Electron transport and anisotropy of the upper critical magnetic field in Ba<Subscript>0.68</Subscript>K<Subscript>0.32</Subscript>Fe<Subscript>2</Subscript>As<Subscript>2</Subscript> single crystals

Early work on the iron-arsenide compounds supported the view, that a reduced dimensionality might be a necessary prerequisite for high-T _c superconductivity. Later, however, it was found that the zero-temperature upper critical magnetic field, H _c2(0), for the 122 iron pnictides is in fact rather isotropic. Here, we report measurements of the temperature dependence of the electrical resistivity, ρ(T), in Ba_0.5K_0.5Fe₂As₂ and Ba_0.68K_0.32Fe₂As₂ single crystals in zero magnetic field and in Ba_0.68K_0.32Fe₂As₂ in static and pulsed magnetic fields up to 60 T. We find that the resistivity of both compounds in zero field is well described by an exponential term due to inter-sheet umklapp electron-phonon scattering between light electrons around the M point to heavy hole sheets at the Γ point in reciprocal space. From our data, we construct an H-T phase diagram for the inter-plane (H | c) and in-plane (H | ab) directions for Ba_0.68K_0.32Fe₂As₂. Contrary to published data for 122 underdoped FeAs compounds, we find that H _c2(T) is in fact anisotropic in optimally doped samples down to low temperatures. The anisotropy parameter, γ = H _c2 ^ab /H _c2 ^c , is about 2.2 at T _c . For both field orientations we find a concave curvature of the H _c2 lines with decreasing anisotropy and saturation towards lower temperature. Taking into account Pauli spin paramagnetism, we perfectly can describe H _c2 and its anisotropy.