S. M. Pershin

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.

Raman spectroscopy of the OH group vibrations in structural complexes of liquid water

A number of spectral features in the structure of the OH band of water located at ∼3450 cm−1 are registered in a series of 34 Raman spectra. Each spectrum of the series is excited by a pair of successive secondharmonic pulses of a moderate intensity (15–20 MW/cm2) from a Nd:YAG laser operating at a pulse repetition frequency of 1 Hz. The pairs of pulses in the series follow at an interval of 15–20 s. It is found that, in ten measurements of the first series, there occur three successively reproduced spectra with an anomalously narrow band (down to 260 cm−1) and spectra with a local minimum in the range of 3400 cm−1. The occurrence of the latter spectra was predicted previously as a manifestation of the occurrence of structural fragments of water. In the range 3690–3700 cm−1, a narrow peak of free OH vibrations is observed, whose intensity decreases in subsequent series. Some Raman spectra are similar to the spectra of the OH vibrations of water clusters in molecular beams and surface layers. These data make it possible to assume that structural complexes exist in the volume of water irradiated by the laser beam, with the lifetime of some of them being no shorter than 40 s.

Spin isomeric selectivity of water molecules upon DNA hydration

Four-photon coherent scattering of laser radiation was used to study the influence of DNA on the content of quasi-free ortho and para isomers of water molecules in its aqueous solution. It was shown that the concentration of quasi-free molecules that form the rotational spectrum of spin isomers increases considerably in the hydration shell of the DNA molecule as compared with pure water. The increase in the concentration of spin isomers occurs disproportionally. In the presence of DNA, the intensity of the rotational spectrum of ortho isomers is on the average much greater than that of para isomers. It was also demonstrated that the character of hydration and the ortho/para ratio change noticeably upon DNA denaturation, which may be evidence of changes in preferable solvation of DNA during its denaturation. The data obtained allowed us to assume that the stability of different biologically important states of macromolecules can be changed by varying the relative concentration of water spin isomers in solution.

Deformation of the Raman scattering spectrum of Ih ice under local laser heating near 0°C

The Raman band of Nd:YAG laser second-harmonic scattering from the O-H stretching vibrations of hexagonal ice was observed to broaden asymmetrically by 90 cm−1 near 0°C with the pulse repetition frequency increasing from 1 to 8 Hz. The center of this band was found to undergo simultaneously a Stokes shift by 25 cm−1. The observed spectral features can be accounted for by the ice being heated by pulsed laser radiation through the electrocaloric effect, because the one-photon absorption mechanism produces a negligible contribution.

Effect of quantum differences of ortho and para H2O spin-isomers on water properties: Biophysical aspect

Quantum differences of ortho/para H2O spin-isomers are considered as a key factor that determines water property taking into account the ortho/para conversion and the unbalanced (1: 1) ortho/para ratio in water. The biophysical mechanism of jump in the permeability of erythrocytes through a microcapillary at 36.6°C in water-based physiological solution and at 37.4°C in heavy water is proposed and discussed.

Four-photon polarization spectroscopy of the rotational resonances in liquids in the range 0–3 THz

The spectra of the coherent molecular rotation that coincide with the rotational spectra of the corresponding molecules in the gas phase are measured for the first time using four-photon coherent laser spectroscopy in the range 0–100 cm−1 in several liquids (CCl4, H2O2, D2O, and H2O). The measured spectra make it possible to separate the spectral contributions of the slow rotational molecular motions about the equilibrium and the fast rotations. The selectivity of the action of the microwave radiation on biological objects can be increased using the results obtained.

Changes in the Raman spectrum of OH stretching vibrations of water in an ultrasonic cavitation field

A modification of the local structure of molecular aggregates in liquid water subjected to the action of an ultrasonic cavitation field is found. This modification is detected by the shift of the center of the Raman band contour of the OH stretching vibrations. It was also found that both the structure and the growth rate of lysozyme crystals grown in redistilled Milli-Q water and in water subjected to cavitation treatment differ considerably from each other.

Preablation electron and lattice dynamics on the silicon surface excited by a femtosecond laser pulse

The study of the time-resolved optical reflection from the silicon surface excited by single femtosecond laser pulses below and near the melting threshold reveals fast (less than 10 ps) Auger recombination of a photogenerated electron–hole plasma with simultaneous energy transfer to the lattice. The acoustic relaxation of the excited surface layer indicates (according to reported data) a characteristic depth of 150 nm of the introduction of the laser radiation energy, which is related to direct linear laser radiation absorption in the photoexcited material due to a decrease in the energy bandgap. The surface temperature, which is probed at a time delay of about 100 ps from the reflection thermomodulation of probe radiation and the integrated continuous thermal emission from the surface, increases with the laser fluence and, thus, favors a nonlinear increase in the fluorescence of sublimated silicon atoms. The surface temperature estimated near the picosecond melting threshold demonstrates a substantial (20%) overheating of the material with respect to the equilibrium melting temperature. Above the melting threshold, the delay of formation of the material melt decreases rapidly (from several tens of picoseconds to several fractions of a picosecond) when the laser fluence and, correspondingly, the surface temperature increase. In the times of acoustic relaxation of the absorbing layer and even later, the time modulation of the optical reflectivity of the material demonstrates acoustic reverberations with an increasing period, which are related to the formation of melt nuclei in the material.

High-resolution four-wave mixing spectroscopy of suspensions: the nonlinear mechanism of a Rayleigh-wing formation

Results of theoretical and experimental investigations of the nonlinear mechanism of Rayleigh-wing formation during the four-wave mixing process in suspensions are presented. The developed theory shows that simultaneous action of two laser radiations with different wavelengths on a spherical particle in a viscous liquid causes a nonlinear resonant response, whose width depends in a complex manner on the particle size, its mechanical properties and the bulk and shear viscosity of the surrounding liquid. The diffusion of particles in a liquid, which depends on several parameters including concentration, leads to concentration dependence of the resonance linewidth observed in the experiment. The four-wave mixing spectroscopy allows us to directly observe nonlinear Rayleigh scattering resonances in the suspensions of spherical nanoparticles whose bandwidth lies in the range from 20 MHz (7 × 10−4 cm−1) to 150 MHz (5 × 10−3 cm−1). These resonances are observed at a high enough level of the detected signal and the signal/noise ratio achieved in the individual measurements is of two orders of magnitude.

Structure of the Raman band of the OH stretching vibrations of water and its evolution in a field of second harmonic pulses of a Nd:YAG laser

A fine structure of the Raman band of the OH stretching vibrations of water at 3450 cm-1 is found upon excitation of the spectra by short trains of second harmonic pulses from a Nd:YAG laser operating at a power of 35 MW/cm2 and a pulse repetition frequency of 1 Hz. An increase in the number of pulses in a train from 2 to 128 or in their power leads to the smoothing and asymmetric narrowing of the band and to the shift of its center toward the low-frequency wing, with a subsequent relaxation to the initial state. The observed dynamics of the Raman spectra in the field of the optical pulses is interpreted as manifestation and evolution of a fluctuating network of hydrogen bonds—the destruction and formation of metastable complexes of water having the characteristic frequencies of OH vibrations. Under normal conditions, the lifetime of these complexes in the state induced by the optical field is no less than 1 s.