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A four-dimensional stochastic approach to dynamics of nuclear fission induced by heavy ions was applied to analyze the key observables from fusion-fission reactions resulted in the highly excited compound nuclei. We took into account not only three shape collective coordinates introduced on the basis of the c, h, α-parametrization but also orientation degree of freedom (K-state) -- spin about the symmetry axis. We systematically investigated the possible deformation dependence of the viscosity coefficient ks predicted by chaos theory and deformation dependence of the γK coefficient deduced by Lestone et al. In the framework of 4D dynamical model, we examined the correlation between dissipation strength and mass, energy and angular distributions of fission fragments. Our calculations demonstrate that the deformation dependent coefficient ks and γK value obtained by Lestone is suitable for simultaneous description of experimental massenergy and angular distributions of fission fragments in 4D model for heavy nuclei, in contrast with the 3D model. The influence of ks and γK parameters on the calculated results could be separated. [ABSTRACT FROM AUTHOR]

The fluorescence of winter and summer furs of ermine (Mustela erminea) taken from the dorsal and ventral parts of the animal body was studied using radiation with λex = 270, 300, 365, 395, and 410 nm. The fur from the ventral part was found to have brighter fluorescence than fur from the dorsal part. Two peaks dominated the fluorescence spectra with λex = 270 and 300 nm. Single-peak fluorescence spectra of winter and summer fur with λex = 365, 395, and 410 nm differed markedly from each other in the peak position and line width. Fluorescence spectra of dorsal and ventral fur were also different. The results could be used to identify ermine skins in collections and items in the absence of other signatures. [ABSTRACT FROM AUTHOR]

A four-dimensional dynamical model was developed and applied to study fission characteristics in a wide range of a fissility parameter. Three collective shape coordinates and the K coordinate were considered dynamically from the ground-state deformation to the scission into fission fragments. A modified one-body mechanism for nuclear dissipation with a reduction coefficient ks of the contribution from a "wall" formula has been used in the study. The inclusion of the K coordinate in the dynamical consideration and use of the "chaos-weighted wall formula" with a deformation-dependent scaling factor ks(q1) lead to fairly good reproduction of the variances of the fission-fragment mass distribution and the prescission neutron multiplicity for a number of fissioning compound nuclei in a wide fissility range. The four-dimensional dynamical calculations describe better experimental prescission neutron multiplicity and variances of fission-fragment mass distribution for heaviest nuclei with respect to a three-dimensional dynamical model, where the K coordinate is assumed to be equal to zero. The estimate of a dissipation coefficient for the orientation degree of freedom, γK ≃ 0.077 (MeV zs)-1/2, is good for heavy nuclei and a larger value of γK ≃ 0.2 (MeVzs)-1/2 is needed for nuclei with mass ACN ≃ 200. [ABSTRACT FROM AUTHOR]

A four-dimensional dynamical model based on Langevin equations was developed and applied to calculate a wide set of experimental observables for the reactions 16O + 208Pb → 224Th and 16O + 232Th → 248Cf over a wide range of excitation energy. The fusion-fission and evaporation residue cross sections, fission fragment mass-energy distribution parameters, prescission neutron multiplicities, and anisotropy of angular distribution of fission fragments could be reasonably reproduced using a modified one-body mechanism for nuclear friction with a reduction coefficient of the contribution from a wall formula ks ≃ 0.25 and a dissipation coefficient for the orientation degree of freedom (K coordinate) γK ≃ 0.077 (MeVzs)-1/2. Inclusion of the K coordinate into calculation of potential energy changes the stiffness of the nucleus with respect to mass asymmetry coordinate for the values of K ≠ 0 and results in a shift of the Businaro-Gallone point towards larger Z2/A values. The experimental data on the fission fragment mass-energy distribution parameters together with mean prescission neutron multiplicity for heavy fissioning nuclei are reproduced through the four-dimensional Langevin calculations more accurately than through three-dimensional calculations. [ABSTRACT FROM AUTHOR]

The triboelectric charging of natural diamond crystals as a result of the contact electrization on a metal surface has been experimentally studied. It is established that the contact electrization of diamond crystals is related to the accumulation of a positive charge due to the filling of hole traps with an activation energy of 1.1–2.17 eV. A physical model is proposed to describe this process. [ABSTRACT FROM AUTHOR]

A macroscopic temperature-dependent model that takes into account nuclear forces of finite range is used to calculate the static and statistical properties of hot rotating compound nuclei. The level-density parameter is approximated by an expression of the leptodermous type. The resulting expansion coefficients are in good agreement with their counterparts proposed previously by A.V. Ignatyuk and his colleagues. The effect of taking simultaneously into account the temperature of a nucleus and its angular momentum on the quantities under study, such as the heights and positions of fission barriers and the effective moments of inertia of nuclei at the barrier, is considered, and the importance of doing this is demonstrated. The fissility parameter (Z2/A)crit and the position of the Businaro–Gallone point are studied versus temperature. It is found that, with increasing temperature, both parameters are shifted to the region of lighter nuclei. It is shown that the inclusion of temperature leads to qualitatively the same effects as the inclusion of the angular momentum of a nucleus, but, quantitatively, thermal excitation leads to smaller effects than rotational excitation.© 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

Results of the development of an industrial technology for the enrichment of the 13C isotope on the basis of the multiphoton dissociation of the molecules of a substance under the action of the radiation of a pulsed CO2 laser are presented. The world's first industrial plant for the 13C enrichment "Uglerod" is described. The physical bases for the effective production of 13C with a concentration higher than 99% are considered. [ABSTRACT FROM AUTHOR]

The multiphoton ionization of (CF3I)nXem mixed clusters formed at the outflow of a mixture of CF3I and Xe from an ultrasonic pulsed nozzle by femtosecond ultraviolet radiation (λ = 266 nm) has been studied. The formation of XeI+ mixed ions and ions in intracluster reactions has been detected. It has been shown that the efficiency of the formation of XeI+ ions significantly depends on the duration of a laser pulse: ultraviolet picosecond radiation is necessary for their formation. The kinetic yield curves of the XeI+ and ions upon ultraviolet multiphoton ionization of (CF3I)nXem mixed clusters have been measured. The characteristic times of their formation determined from these curves are (53 ± 8) ps and (65 ± 6) ps, respectively. [ABSTRACT FROM AUTHOR]

Ultrafast electron microscopy (UEM) has made it possible to visualize laser-induced time-dependent processes in materials with a high spatial and temporal resolution. This analytical method is based on sample excitation (pumping) by a pulsed laser beam and its probing by time-synchronized photoelectron bunches in a transmission electron microscope column. Using a digital 2D detector in an experimental setup, one can record a "molecular movie" as a sequence of images representing the behavior of material in the space–time continuum. High temporal resolution is of particular interest in the problems related to detailed analysis of various laser-induced transient processes occurring in thin films, observation of the response of adsorbed molecules to nonequilibrium structural changes of the surface, surface and volume dynamics in semiconductors, generation of coherent acoustic and optical phonons, surface melting of nanoparticles, and nonequilibrium structural dynamics of phase transformations. This review presents the state of the art of the UEM method, where picosecond, femtosecond, and subfemtosecond probe pulses are used to reveal the structural dynamics of condensed matter. [ABSTRACT FROM AUTHOR]

Electron-pulse probing of fast laser-induced processes has allowed the direct observation of the structural dynamics in matter with a high spatiotemporal resolution. A thin gold film has appeared to be a convenient photocathode, and photoelectron emission has been induced by femtosecond ultraviolet radiation with a photon energy of about 4.65–4.75 eV (in particular, ω 4.65 eV for the third harmonic of the Ti:sapphire laser). For the linear photoelectric effect, this energy contradicts the reference work function WAu 5.1–5.3 eV of pure metal. Reasons for such contradiction have been analyzed and good agreement with experimental data has been reached with a model proposed for the generation of photoelectron pulses. [ABSTRACT FROM AUTHOR]

The review covers recent developments and achievements in the dynamical description of fission process at high excitation energy. It is shown that the dynamical approach based on multidimensional Langevin equations combined with the statistical description of nuclear decay by particles evaporation is capable of fairly well describing the formation of fission fragment mass-energy, charge, and angular distributions of fission fragments in coincidence with the pre- and post-scission particle emission. The final yields of fission and evaporation residues channels products could be obtained. The detailed description of fission dynamics allows studying different stages of fission process, indicating the most important ingredients governing fission process and studying in detail such fundamental nuclear properties as nuclear viscosity and fission timescale. The tasks and perspectives of multidimensional dynamical approach are also discussed. [ABSTRACT FROM AUTHOR]

The behavior of a thin-film GeTe crystal induced by intense femtosecond laser pulses ( μm) has been studied using a pulsed electron diffractometer. The sample is an annealed 20-nm GeTe film on a copper grid with a carbon coating. It has been found that laser ablation results in the formation of an ultrathin GeTe crystal (assumingly, GeTe monolayer) with a high radiation resistance. Possible reasons for the detected nanosize effect are discussed. [ABSTRACT FROM AUTHOR]

Collisional radiative involvement of molecules not absorbing IR laser radiation into resonance with a laser field has been investigated for the case when nonabsorbing and absorbing molecules are laser-irradiated in a two-component medium. Experiments have been conducted with a CF2HCl/CF3Br mixture at a 1/1 pressure ratio. Molecules have been excited by a pulsed CO2 laser. Two types of experiments have been considered: (i) molecules were irradiated under nonequilibrium thermodynamic conditions due to a compression shock wave arising before the solid surface when it was subjected to a supersonic pulsed gasdynamically cooled molecular flux and (ii) molecules were irradiated under static conditions with a gas in the cell kept at room temperature. It has been found that when molecules vibrationally cooled in the compression shock wave (in this case, their IR absorption bands are narrow; the FWHM is 7–8 cm–1) are irradiated, initially nonabsorbing CF2HCl molecules get effectively involved into resonance with the laser field. Their effective dissociation (with dissociation yield β ≥ 10–15%) has been discovered when the CF2HCl/CF3Br mixture was irradiated under the condition of CO2 laser frequency detuning by more than 15–25 cm–1 from the center of the IR absorption band of molecules vibrationally cooled in the compression shock wave. If molecules are irradiated at room temperature (the gas temperature in the cell), in which case the IR absorption band of molecules is rather wide (25–30 cm–1), the collisional radiative involvement of CF2HCl molecules into interaction with the laser field, albeit less pronounced, persists. [ABSTRACT FROM AUTHOR]

The formation mechanism of the selectivity of IR laser isomerization induced by vibrational multiphoton excitation is considered. The effective and highly selective isomerization of perfluorodimethyl ketene (CF)C=C=O into perfluoromethacrylic acid fluoride FC=C(CF)COF and perfluorocyclobutene into perfluorobutadiene upon pulse irradiation with a CO laser and its second harmonic was performed. The conversion of (CF)C=C=O into FC=C(CF)COF was higher than 99%. A record-breaking conversion of 99.8% of the parent substance into the isomer was achieved in the case of perfluorocyclobutene isomerization into perfluorobutadiene. It was shown that the high selectivity of the laser-induced chemical reactions is mainly associated with the different levels of the vibrational excitation of the parent molecules and their isomers. The latter is due to the difference in the IR absorption spectra of different isomers, which allows for the excitation of the necessary component with a high selectivity. [ABSTRACT FROM AUTHOR]

We have studied the dynamics of intramolecular vibrational redistribution (IVR) from the initially excited mode v ≈ 3330 cm (acetylene-type H-C bond) in H-C≡C-CF molecules in the gaseous phase by means of anti-Stokes spontaneous Raman scattering. The time constant of this process is estimated as 2.3 ns-this is the slowest IVR time reported so far for the room-temperature gases. It is suggested that so long IVR time with respect to the other propyne derivatives can be explained by a larger defect, in this case, of the Fermi resonance of v with v + 2v-the most probable doorway state leading to IVR from v to the bath of all vibrational-rotational states with the close energies. In addition, it is shown that the observed dynamics is in agreement with a theoretical model assuming strong vibrational-rotational mixing. [ABSTRACT FROM AUTHOR]

The results of investigation of dissociation of (CF3I) n clusters upon resonant excitation of vibrations of CF3I molecules by pulsed CO2 laser radiation are reported. The kinetics of dissociation of such clusters is studied and the dissociation yield is measured. It is shown that its value is completely controlled by fluence ΦIR of transmitted IR radiation energy and its time dependence is exponential. The results of measurements show that the dissociation lifetime of clusters is shorter than 10−8 s. The velocity and translational temperature of free CF3I molecules formed during dissociation of clusters are measured, as well as the dependence of these parameters on ΦIR. It is concluded that, under these conditions of IR excitations, the dissociation of (CF3I) n clusters can be treated as consecutive evaporation of molecules. [ABSTRACT FROM AUTHOR]

We report about effective ionization of iodine atoms and CF3I molecules under the action of intense XeCl laser radiation (308 nm). The only ion fragment resulting from the irradiation of the CF3I molecules is the I+ ion. We have studied the influence of the intensity, spectral composition, and polarization of the laser radiation used on the intensity of the ion signal and the shape of its time-of-flight peak. Based on the analysis of the results obtained, we have suggested the mechanism of this effect. The conclusion drawn is that the ionization of the iodine atoms by the ordinary XeCl laser with a nonselective cavity results from a three- (2 + 1)-photon REMPI process. This process is in turn due to the presence of accidental two-photon resonances between various spectral components of the laser radiation and the corresponding intermediate excited states of the iodine atom. The probability of ionization of the atoms from their ground state I(2P3/2) by the radiation of the ordinary XeCl laser is more than two orders of magnitude higher than the probability of their ionization from the metastable state I*(2P1/2). The ionization of the CF3I molecules by the XeCl laser radiation occurs as a result of a four-photon process involving the preliminary one-photon dissociation of these molecules and the subsequent (2 + 1)-photon REMPI of the resultant neutral iodine atoms. [ABSTRACT FROM AUTHOR]

The dynamics of intramolecular vibrational energy redistribution from the initially excited νHC mode in the propyne molecule (H-C≡C-CH3), as well as in three its derivatives that are obtained by replacing one of the hydrogen atoms of the methyl group with the chlorine atom (propargylchloride), the OH radical (propargyl alcohol), or with the NH2 radical (propargylamine), has been studied. Probing was performed by anti-Stokes spontaneous Raman scattering. The measured values of the deexcitation rate W of the νHC mode lie in the range 109−1010 s−1. A significant feature of the dynamics—an incomplete energy redistribution from the νHC mode—is especially clearly pronounced for the H-C≡C-CH3 and H-C≡C-CH2Cl molecules, for which the values of the relative level σ of the residual energy in the νHC mode are approximately equal to 0.54 and 0.25, respectively. A theoretical analysis performed made it possible to relate the parameters W and σ, on the one hand, and the density ρ of the so-called bath states, which are responsible for the vibrational energy redistribution, on the other hand. It is shown that, for all the four molecules considered, the required values of ρ can be accounted for solely by a strong vibrational-rotational mixing in the bath, as a result of which the projection of the total angular momentum onto the axis of the molecule ceases to be “good” quantum number. [ABSTRACT FROM AUTHOR]

The results of experimental studies of multiphoton ionization of CF2HCl molecules and clusters by UV laser radiation in the wavelength range 217–236 nm are reported. In the case of molecules, the main reaction products are CF2H+ and CF+ ions as well as atomic chlorine. It is found that the spectra of the products of ionization of free molecules and molecules condensed into clusters differ qualitatively: multiphoton ionization of clusters does not yield CF2H+ ions. The dependences of the ion yield on the intensity of laser radiation and its wavelength are measured. The effect of a constant electric field and the radiation spectral width on the multiphoton ionization process is demonstrated. The shape of the velocity distributions is determined for a number of products. A strong anisotropy is detected in the reaction of formation of CF2H+ ions. Possible mechanisms for these processes are discussed. [ABSTRACT FROM AUTHOR]

The clustering of CF2HCl (Freon-22 refrigerant) molecules is found to take place when these molecules are dynamically cooled in a pulsed supersonic beam. A method of CF2HCl cluster beam diagnostics is developed that combines UV multiphoton ionization, time-of-flight mass spectroscopy, and cluster IR photodissociation. The velocity of directed motion of (CH2HCl)n clusters, as well as the longitudinal and transverse velocities of their thermal motion, are measured at different stagnation pressures P0. The cluster mean size and the degree of clustering in the flow are estimated depending on supersonic flow conditions. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

IR multiphoton dissociation of trichlorosilane molecules in scavenger gas (O2, CO2, OCS, halomethanes, BCl3, TiCl4, etc.) media was studied. Stable, volatile dissociation products were determined. It was shown that the product formation mechanism depends on the partial pressure of SiHCl3. At a high pressure (≥400–800 Pa) of SiHCl3, its photolysis in a mixture with fluorine-, chlorine-, or bromine-containing scavengers led to the formation of products of the SiF4 – nCln and SiBr4 – nCln type, where n = 1–4. An SiHCl3 conversion into SiCl4 higher than 70% could be achieved. The formation mechanism was proposed for the photolysis products. At a low SiHCl3 pressure (<70 Pa), the formation of a stable volatile product was observed only in a mixture with BCl3, which resulted from the reaction of insertion of SiCl2 in the B–Cl bond. [ABSTRACT FROM AUTHOR]

Intramolecular vibrational redistribution (IVR) from the terminal acetylene mode νHC has been studied for four molecules: H–C=C–CH3 (propyne), H–C=C–CH2Cl (propargyl chloride), H–C=C–CH2OH (propargyl alcohol), and H–C=C–CH2NH2 (propargyl amine). The experiments were performed with the room-temperature gases. The transition |0>→|1> in the mode νHC was pumped by a short laser pulse. Anti-Stokes spontaneous Raman scattering was used as a probe. The measured parameters were the de-excitation rate W and the dilution factor σ defined as the relative level of the residual energy in the νHC mode at long pump-probe delay times. The pair of these values {W,σ} allowed us to determine the density ρeff of those vibrational-rotational states, which are involved in IVR from state |1>. For two molecules, HCCCH3 and HCCCH2Cl, the experimental results were consistent with the suggestion that all close vibrational-rotational states with the same total angular momentum J and symmetry participate in the IVR regardless of the other rotator quantum number K (in the case of HCCCH3) or Ka (in the case of HCCCH2Cl) and the vibrational quantum numbers as well. For the other two molecules, HCCCH2OH and HCCCH2NH2, this effect was also present, yet the experimental results revealed certain restrictions. We have obtained a satisfactory theoretical fit with the assumption that the low-frequency torsion vibration of the hydrogen atom in the hydroxyl group (in the case of HCCCH2OH) or hydrogen atoms in the amine group (in the case of HCCCH2NH2) does not participate in the IVR. This assumption can be treated as a challenge to future studies of these molecules by high-resolution spectroscopy and various double-resonance and pump-probe techniques. [ABSTRACT FROM AUTHOR]

The coherent lattice dynamics in thin crystalline Sb and Bi films has been investigated using ultrafast electron diffraction. The samples were exposed to Ti:sapphire femtosecond laser radiation and probed by ultrashort electron pulses. The registered generation of coherent optical phonons in the crystals corresponded to the A1g and Eg modes and their combinations in Sb, as well as to the manifestation of the A1g mode and its first and second overtones in Bi. Detection of optical phonons with frequencies of up to 9 THz indicated that a temporal resolution at a level of ~100 fs was obtained. An ultrafast electron diffractometer for studying nonlinear laser-induced processes in molecular and cluster beams has been developed based on a femtosecond electron source. [ABSTRACT FROM AUTHOR]

The dynamics of intramolecular vibrational-energy redistribution from an initially excited mode ν1 (the acetylene-type H–C bond) to the other modes of the H–C≡C–Si(CH3)3 molecule was studied experimentally. Probing was performed by spontaneous anti-Stokes Raman scattering. The measured deexcitation time of ν1 was 128±10 ps. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

We present the results of an investigation into the interaction of SF6 molecules and clusters in a molecular beam with resonant IR laser radiation at different stages of the beam evolution along the axis of its propagation. The beam has been formed as a result of gas-dynamic expansion of a mixture of SF6 with argon carrier gas during expansion from a pulsed nozzle. The experimental setup and the investigation method are described. It has been shown that selective vibrational excitation of SF6 molecules with a specific sulfur isotope by a CO2 laser near the nozzle edge causes suppression of the clustering process of these isotopic molecules. Selective IR excitation of clusters under the conditions of the formed cluster beam leads to isotopically selective dissociation of clusters. Depending on the experimental conditions including different distances of the irradiation zone of particles from the nozzle edge, the results of measuring the efficiency and selectivity of molecular clustering suppression and cluster dissociation processes are presented. It has been shown that both of these processes make it possible to achieve high selectivity values for the 32S and 34S sulfur isotopes. In the case in which the clustering of SF6 molecules was selectively suppressed, selectivity values α ≥ 25–30 have been obtained. Upon selective dissociation of (SF6)2 dimers under similar expansion conditions of the gas mixture, selectivity values α ≥ 20–25 for 32SF632SF6 dimers with respect to 34SF632SF6 dimers have been obtained. Particular attention has been paid to measurements at a high dilution of SF6 in argon under conditions of predominant formation of (SF6)mArn mixed clusters. The potential of using studied processes as a basis for the technology of the laser isotope separation are discussed. [ABSTRACT FROM AUTHOR]

Direct methods of imaging of the substance that was excited by a femtosecond laser in the space–time continuum, which are based on the sensing of the sample by ultrashort electron bunches, strictly synchronized with femtosecond laser pulses, have been demonstrated. A number of experiments in the field of ultrafast electron microscopy and diffraction performed at the Institute of Spectroscopy of the Russian Academy of Sciences has been presented. [ABSTRACT FROM AUTHOR]

We have measured the ultrafast anisotropic optical response of highly doped graphene to an intense single cycle terahertz pulse. The time profile of the terahertz-induced anisotropy signal at 800 nm has minima and maxima repeating those of the pump terahertz electric field modulus. It grows with increasing carrier density and demonstrates a specific nonlinear dependence on the electric field strength. To describe the signal, we have developed a theoretical model that is based on the energy and momentum balance equations and takes into account optical phonons of graphene and the substrate. According to the theory, the anisotropic response is caused by the displacement of the electronic momentum distribution from zero momentum induced by the pump electric field in combination with polarization dependence of the matrix elements of interband optical transitions. [ABSTRACT FROM AUTHOR]

A common strategy aimed at achieving a high temporal resolution in ultrafast electron microscopy and diffraction is based on the use of strong electrostatic fields in the accelerating gap to form fast electron pulses of ultrashort duration. In this work, the dynamics of the propagation of ultrashort photoelectron bunches is studied taking into account the time-of-flight chromatic aberration: the spread-out of electron pulses at the exit from the region of the accelerating electric field. The results of the calculation of the duration of photoelectron pulses taking into account Coulomb repulsion are presented. According to the analysis, the use of strong electrostatic fields in the accelerating gap for the formation of fast electron pulses of ultrashort duration is not a necessary condition for achieving the final high temporal resolution in the method of ultrafast electron microscopy. The modes of operation of ultrafast transmission electron microscope were found for which the temporal resolution increases with the growth of time-of-flight chromatic aberration. [ABSTRACT FROM AUTHOR]

The results of studies on the isotope-selective dissociation of homogeneous and mixed van der Waals (SF6)mArn clusters induced by infrared laser radiation are presented. The method is based on the selective vibrational excitation of clusters by an infrared laser, which leads to their heating and dissociation. An experimental setup and procedure are described. The results of measurements of the efficiency and selectivity of cluster dissociation at different pressures and gas compositions above the nozzle, as well as various parameters of laser radiation, are presented. The dependences of the efficiency and selectivity of cluster dissociation on the frequency and power of the exciting laser radiation on the composition and pressure of gas above the nozzle, as well as on the distance of the irradiation zone of the particles on the nozzle exit are obtained. It is shown that the frequency of laser radiation and the composition and pressure of gas above the nozzle significantly affect the parameters of selective infrared dissociation of clusters. Experiments on isotope-selective dissociation of both homogeneous (SF6)m clusters and mixed (SF6)mArn clusters are performed. It was found that, with the dissociation of (SF6)mArn clusters, a rather high selectivity can be reached. Thus, in the case of an SF6/Ar mixture at a pressure ratio of 1/200, for the selectivity of dissociation of (32SF6)2 clusters with respect to SF6 clusters, the values ≥10–20 are obtained under conditions of irradiation by a beam on the 10P(32) laser line (at a frequency of 932.96 cm–1). Conditions are found when the values of efficiency and selectivity of dissociation of homogeneous (SF6)m clusters and mixed (SF6)mArn clusters are optimal. [ABSTRACT FROM AUTHOR]

Abstract—: The vertical component of the electric field Ez in the hydrosphere is not contaminated by the telluric component and therefore can effectively be used to monitor various processes in the hydrosphere itself, lithosphere, and atmosphere. For this purpose, the Ez monitoring experiment on the surface-floor base has been conducted in Lake Baikal since 2003. The lack of the telluric component is confirmed experimentally and justified by simulation. The effect and precursors of the close earthquake, the variations in total flows of water currents, and variations in the closing current of the Global Electric Circuit in the conducting Earth are studied. The measurements of macroscopic quantum nonlocal correlations have also been set up since 2012. Based on them, the possibility of forecasting processes with a large random component, in particular a remote earthquake, is demonstrated. On the territory adjacent to the deep-water monitoring site, measurements of the gradients of magnetic field variations have been underway since 2017; it is expected that these will be expanded to the entire coast of Lake Baikal. To interpret measurements, geoelectric models of the Baikal rift, which represent the known competing hypotheses, have been constructed. [ABSTRACT FROM AUTHOR]

The modification of a graphene sheet, which was fabricated by chemical vapor deposition on a close-meshed copper grid, during powerful femtosecond laser irradiation is studied. The process of long-term irradiation of a sample in vacuum is found to be accompanied by (1) breaking carbon bonds, which is indicated by a decrease in the intensities of the reflections corresponding to electron-beam diffraction by graphene and (2) the formation of new products, which is indicated by the appearance of new diffraction rings and a change in the Raman spectrum of the sample. The compositions of the forming chemical compounds are analyzed. Copper oxides Cu2O and CuO are shown to form predominantly on the sample surface as a result of the chemical reactions induced by powerful femtosecond laser pulses. [ABSTRACT FROM AUTHOR]

The infrared (IR) laser radiation control of the clustering of CF3Br molecules during the gas-dynamic expansion of a CF3Br/Ar mixture at the exit from a nozzle is investigated. Prominence is given to studying the possibility of bromine-isotope-selective suppression of the clustering of CF3Br molecules due to their resonance vibrational excitation in the gas-dynamic expansion zone near the nozzle. A continuous CO2 laser is used in experiments to excite molecules and clusters in a beam, and a quadrupole mass spectrometer is used to detect them. The experimental setup and the experimental technique are described. The dependences of the efficiency of molecule clustering suppression on the exciting laser radiation parameters, the gas parameters (composition, pressure) above the nozzle, and the distance from the nozzle exit section to a molecule irradiation zone are obtained. Bromine-isotope-selective suppression of molecule clustering is shown to occur at the exit from the nozzle due to the resonance vibrational excitation of gas-dynamically cooled CF3Br molecules. When CF3Br/Ar mixtures are used at pressure ratios p(CF3Br): p(Ar) = 1: 10 and 1: 30, the enrichment of a cluster beam by bromine isotopes are Kenr(81Br) ≈ 1.18 ± 0.09 and 1.12 ± 0.07 during the 9R(30) laser line (1084.635 cm-1) irradiation of a jet. The clustering suppression selectivity is α ≈ 1.18 when the mixture at the pressure ratio p(CF3Br): p(Ar) = 1: 10 is used. These results suggest that the proposed method can selectively control the clustering of the molecules containing the heavy element isotopes that have a small isotope shift in IR absorption spectra (OsO4, WF6, UF6). [ABSTRACT FROM AUTHOR]

The dynamics of dissociation of (IF2CCOF) n , (CF3I) n , and (CH3I) n clusters induced by femtosecond UV radiation (λ = 266 nm) is investigated. The method of UV excitation and photoionization probing (λ = 400 nm) combined with the time-of-flight mass spectrometry is applied. It is found that clusters excited to Rydberg states lying below the ionization threshold are decomposed, as a result of subsequent relaxation processes, giving rise to free neutral molecules. A mechanism of electronic–vibrational relaxation process is proposed, and data on the characteristic times of different stages of this process are obtained. [ABSTRACT FROM AUTHOR]

The control of clustering in molecular beams with the help of IR lasers is experimentally studied. Studies were performed with a molecular CFI gas diluted with argon or xenon using a cw CO laser. The control of clustering is based on the resonance vibrational excitation of molecules or clusters by the IR laser radiation near the nozzle exit. Depending on the distance from the excitation region to the nozzle cut, the irradiation of the molecular beam either suppresses the clustering of resonantly excited molecules (when the beam is irradiated near the nozzle exit where clustering occurs) or causes the dissociation of small clusters (when the beam is irradiated away from the nozzle where clustering is at the growth stage). The suppression of molecular clustering and the dissociation of clusters in beams were studied by measuring and analyzing the integrated intensities of ion peaks of cluster fragments with a time-of-flight spectrometer. The efficiencies of clustering suppression and cluster dissociation were studied as functions of exciting laser radiation parameters, the beam irradiation geometry, gas parameters over the nozzle, and the nozzle construction. It is shown that the efficiencies of clustering suppression and cluster dissociation strongly depend on the exciting laser radiation intensity, the nozzle construction, and the distance from the irradiation region to the nozzle cut. Parameters providing the most efficient control of clustering suppression and cluster dissociation are found. [ABSTRACT FROM AUTHOR]

The generation of coherent optical phonons in a polycrystalline antimony film sample has been investigated using femtosecond electron diffraction method. Phonon vibrations have been induced in the Sb sample by the main harmonic of a femtosecond Ti:Sa laser (λ = 800 nm) and probed by a pulsed ultrashort photoelectron beam synchronized with the pump laser. The diffraction patterns recorded at different times relative to the pump laser pulse display oscillations of electron diffraction intensity corresponding to the frequencies of vibrations of optical phonons: totally symmetric ( A ) and twofold degenerate ( E ) phonon modes. The frequencies that correspond to combinations of these phonon modes in the Sb sample have also been experimentally observed. [ABSTRACT FROM AUTHOR]

The composition and content of pulsed neutral cluster beams are determined by a specially proposed method from ion signals of cluster fragments in time-of-flight spectra of clusters in these beams. For beams of different-size mixed clusters (SF)Ar (where 1 ≤ m ≤ 4 and 0 ≤ n ≤ 9 are the number of molecules and atoms in clusters, respectively), it is shown that the proposed method makes it possible to determine the composition and content of neutral van der Waals molecular and atomic-molecular clusters in beams. [ABSTRACT FROM AUTHOR]

The generation of coherent optical phonons in an antimony film has been directly observed by the femtosecond electron diffraction method. The sample has been excited by a femtosecond laser pulse (λ = 800 nm) and probed with a pulsed photoelectron beam. Oscillations of the intensity corresponding to vibration frequencies of optical phonons excited by the laser have been observed in the obtained diffraction patterns: totally symmetric ( A) and twofold degenerate ( E) phonon modes of antimony and their combinations. [ABSTRACT FROM AUTHOR]

The dynamics of photoprocesses induced by femtosecond infrared radiation in free Fe(CO) molecules and their clusters owing to the resonant excitation of vibrations of CO bonds in the 5-μm range has been studied. The technique of infrared excitation and photoionization probing (λ = 400 nm) by femtosecond pulses has been used in combination with time-of-flight mass spectrometry. It has been found that an infrared pulse selectively excites vibrations of CO bonds in free molecules, which results in a decrease in the yield of the Fe(CO) molecular ion. Subsequent relaxation processes have been analyzed and the results have been interpreted. The time of the energy transfer from excited vibrations to other vibrations of the molecule owing to intramolecular relaxation has been measured. The dynamics of dissociation of [Fe(CO)] clusters irradiated by femtosecond infrared radiation has been studied. The time dependence of the yield of free molecules has been measured under different infrared laser excitation conditions. We have proposed a model that well describes the results of the experiment and makes it possible, in particular, to calculate the profile of variation of the temperature of clusters within the 'evaporation ensemble' concept. The intramolecular and intracluster vibrational relaxation rates in [Fe(CO)] clusters have been estimated. [ABSTRACT FROM AUTHOR]

The fragmentation of free homogeneous (CFI) clusters in a molecular beam ( n ≤ 45 is the average number of molecules in the cluster) and (CFI) clusters inside or on the surface of large (Xe) clusters ( m ≥ 100 is the average number of atoms in the cluster) by ultraviolet and infrared laser radiations has been studied. These three types of (CFI) clusters are shown to have different stabilities with respect to fragmentation by both ultraviolet and infrared radiations and completely different dependences of the fragmentation probability on the energy of ultraviolet and infrared radiations. When exposed to ultraviolet radiation, the free (CFI) clusters fragment at comparatively low fluences (Φ ≤ 0.15 J cm) and the weakest energy dependence of the fragmentation probability is observed for them. A stronger energy dependence of the fragmentation probability is observed for the (CFI) clusters localized inside (Xe) clusters, and the strongest dependence is observed for the (CFI) clusters located on the surface of (Xe) clusters. When the clusters are exposed to infrared radiation, the homogeneous (CFI) clusters efficiently fragment at low fluences (Φ ≤ 25 mJ cm), higher fluences (Φ ≈ 75 mJ cm) are needed for the fragmentation of the (CFI) localized inside (Xe) clusters, and even higher fluences (Φ ≈ 150 mJ cm) are needed for the fragmentation of the (CFI) clusters located on the surface of (Xe) clusters. It has been established that small (CFI) clusters located on the surface of (Xe) clusters do not fragment up to fluences Φ ≈ 250 mJ cm. The fragmentation efficiency of (CFI) clusters is shown to be the same (at the same fluence) when they are excited by both pulsed (τ ≈ 150 ns) and continuous-wave infrared laser radiations. Possible causes of such a pattern of ultraviolet and infrared laser-induced fragmentation of these clusters are discussed. [ABSTRACT FROM AUTHOR]

The fragmentation of homogeneous (CFI) clusters (where n ≤ 45 is the average number of molecules in a cluster) in a molecular beam, as well as (CFI) clusters inside of large (Xe) clusters (where m ≥ 100 is the average number of atoms in a cluster) or on their surface, by laser ultraviolet radiation has been studied. It has been found that the indicated three types of (CFI) clusters have different stabilities with respect to fragmentation and strongly different dependences of the fragmentation probability on the energy of ultraviolet radiation. Fragmentation at low energies and the weakest energy dependence of the probability of fragmentation are observed for homogeneous clusters, a stronger dependence is characteristic of (CFI) clusters localized inside (Xe) clusters, and the strongest dependence is observed for (CFI) clusters on the surface of (Xe) clusters. Possible reasons for such a character of the observed dependences have been discussed. [ABSTRACT FROM AUTHOR]

The excitation and ionization of CFI molecules and their clusters by femtosecond UV laser pulses is studied. It is concluded that the types of excitation of free CFI molecules and their clusters by femtosecond UV laser pulses are different. The composition and kinetic energy of ion products observed upon the ionization of (CFI) clusters by femtosecond pulses are found to differ considerably from those obtained upon ionization by nanosecond pulses. It is shown that the molecular I ion is produced in reactions induced in (CFI) clusters by UV radiation. Using the pump-probe method, we found the two channels of producing I ions with characteristic times τ ≈ 1 ps and τ ≈ 7 ps. A model of the reactions under study proposed in the paper is consistent with our experimental results. [ABSTRACT FROM AUTHOR]

Intracluster reactions that are induced in (CFI) clusters by femtosecond ultraviolet radiation, including the reaction of the formation of the I molecular ion, have been directly observed. It has been shown that there are two channels of the formation of I ions with the characteristic times τ ≈ 1 ps and τ ≈ 7 ps. A model of these reactions has been proposed that is in good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

The results of the investigation of the multiphoton ionization of (CFI) clusters by ultraviolet laser radiation are reported. The yields of the I and I ions, which are the products of the multiphoton ionization, have been measured as functions of the intensity of the ultraviolet radiation at the wavelengths of 308 and 232.5 nm. The degree of multiphoton ionization has been determined and appears to depend on the wavelength of radiation. The velocity distributions of the products have been measured in detail for various wavelengths and various polarizations of radiation. The anisotropy parameters of the velocity distributions of the produced ions and their kinetic energy have been determined. After analysis of the data, a mechanism of the multiphoton ultraviolet ionization of the clusters under investigation has been proposed. This mechanism depends on the used wavelengths. [ABSTRACT FROM AUTHOR]

The dynamics of multiphoton excitation of (CF)CCO molecules has been investigated under the condition of resonant action of femtosecond infrared laser radiation on the ν vibrational mode of the C=C=O bond. It has been shown that the mode-selective excitation of this vibration occurs up to the ν = 6 level. The kinetics of the subsequent intramolecular vibrational energy redistribution from the ν mode has been measured. A value of 5 ± 0.3 ps has been obtained for the characteristic time of this process. [ABSTRACT FROM AUTHOR]

The resonant vibrational excitation of gaseous iron pentacarbonyl Fe(CO)5 by femtosecond pulsed IR laser radiation is accompanied by the deposition of microcrystals of higher iron carbonyls Fe2(CO)9 and Fe3(CO)12. It is found that microstructured iron-containing films are formed on the surface of the gas-cell windows immediately in the region of laser beam passage. The possible mechanism of film formation is considered. [ABSTRACT FROM AUTHOR]

The one-photon IR excitation and subsequent UV dissociation of ammonia molecules selective with respect to nitrogen isotopes were studied. The selectivity of vibrational excitation is achieved by tuning CO2 laser radiation to resonance with 14NH3 or 15NH3 molecules. The dependences of the yield of dissociation for each isotopic component and the selectivity on the buffer gas (N2, O2, Ar) pressure, the partial pressure of ammonia, and the time of delay between IR and UV laser pulses were established. At low pressures (67–270 Pa) of the isotopic mixture with a 15N concentration of 4.8%, the dissociation selectivity for 15N was 17. The mechanisms responsible for the selectivity of IR + UV-initiated dissociation are discussed. The phenomenological model has been developed that takes into consideration the effect of the interisotopic V-V exchange and V-T relaxation on the formation of the yield and selectivity of the two-stage IR+UV dissociation of ammonia. [ABSTRACT FROM AUTHOR]

Presents an obituary for physicist Roman Ivanovich Personov.