Recovering the rotational density matrix of a molecular ensemble from time-resolved angular distributions is central to understanding ultrafast rotational dynamics, yet the inverse problem is severely underdetermined. We analyze the forward operator that maps the density matrix of laser-aligned symmetric-top molecules to the angular distribution retrieved in pump-probe experiments and demonstrate through singular value decomposition that 74%-88% of the real density matrix unknowns lie in the null space for maximum angular momentum quantum numbers Jmax = 2-5. This rank deficiency is intrinsic to the measurement geometry and imposes a linear lower bound on reconstruction error: the minimum-norm least-squares (pseudoinverse) solution sets all null-space components to zero, establishing the best achievable error for any linear, unbiased estimator. Nonlinear constraints-positive semidefiniteness, trace conservation, and block symmetries-partially recover null-space information, but the residual error grows with Jmax, reaching 15%-44% for Jmax = 5. We present a two-stage pipeline in which a convolutional neural network trained on simulated data provides a warm start for the fast iterative shrinkage-thresholding algorithm. For both CF3I and CH3Cl across Jmax = 2-6, this approach reduces the Frobenius reconstruction error by 80%-99% relative to optimization from thermal equilibrium, maintaining stable errors of 0.5%-1.1% as Jmax increases. The pipeline is robust to data noise down to a 20 dB signal-to-noise ratio and operates ten times faster than the baseline and outperforms the maximum-entropy approach by a factor of 15-39×. The classical iterative quantum tomography algorithm becomes numerically unstable for Jmax ≥ 4, whereas the proposed method converges reliably at all tested truncation levels.

The use of short photoelectron pulses, pioneered in the 1980s, opened up the possibility of studying structural dynamics with high spatiotemporal resolution. The combination of nano-pico-femtosecond lasers with electron-based technology has become extremely fruitful for observing the behavior of atoms and molecules on their natural length and time scales. In imaging mode, this concept soon led to the creation of 4D transmission electron microscopy. In the electron diffraction mode, the achievement of ultrabright electron sources provided a unique opportunity to shoot molecular movies with atomic resolution. These sources are at their fundamental space charge limit with sufficient brightness to literally light up atomic motions. The high sensitivity of this approach, combined with low radiation damage, made it possible to atomically resolve reaction dynamics with nanograms of material. In contrast to the X-ray free electron lasers (XFELs), the development of ultrabright electron sources made it possible to conduct experiments on very thin films of promising materials in small-scale facilities in standard laboratories. The extension to quantum tomography has recently opened a new page in the study of matter using short electron bunches. Here we review the development of ultrafast transmission electron microscopy and diffraction techniques that enable detection of structural dynamics on the primary timescales.

Ultrafast electron diffraction (UED) is used to study laser-induced processes in a free-standing ti 50 nm-thick film of gold single crystal. The sample is pumped by 515-nm fs laser pulses with incident fluence of ti9 mJ/cm2 and probed by time-delayed fs electron pulses with an energy of 47 keV. The Debye-Waller formalism is used to directly map the time dependence of the crystal lattice temperature. Based on the experimental data, the electron-phonon coupling constant for Au is estimated, which is in agreement with the literature data. By analyzing the electron-diffraction kinetics, it was possible to visualize coherent shear acoustic oscillations in gold. A new methodology is presented, which allows estimating the melting conditions of crystals induced by short laser pulses. It is based on the observation of reversible structural dynamics in a non-destructive manner using a low-intensity pulsed electron probe.

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, ħ 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.

One of the most attractive molecular systems in the world of chemistry and medicine is vitamin B12, which was originally discovered as a factor against deficiency (pernicious) anemia. Deficiency of this essential vitamin leads to a decrease in the number of red blood cells in the blood and a drop in hemoglobin levels. The article provides a brief overview of the processes leading to the destruction of vitamin B12 caused by hypoxia, the action hypochlorous acid, superoxide anion radical, hydrogen peroxide, hydroxyl radical, peroxynitrite. Under conditions of hypoxia, oxygen transport in the electron transport chain may be disrupted, resulting in the reduction of oxygen on ubiquinone to a superoxide radical under the action of electrons that have not reached cytochrome oxidase. Oxidative stress develops, during which oxygen-containing radicals are formed, which can cause irreversible changes in the vitamin and lead to loss of biological activity. Hydrogen peroxide formed as a result of step-by-step protonation of the formed superoxide-anion radicals can act as such oxidants. Hydrogen peroxide, in turn, is capable of reacting with metals of variable oxidation state to form a reactive hydroxyl radical, producing the Fenton reaction. In addition, hypochlorous acid formed by the enzyme myeloperoxidase in the presence of hydrogen peroxide and chloride anion, as well as peroxynitrite, an active oxidant obtained by reacting the superoxide–anion radical with nitrogen (II) oxide, can act as oxidants. The latter is produced in large quantities under hypoxia conditions due to an increase in the activity of endothelial nitric oxide synthetase. The publications devoted to the influence of various oxidants on the stability of vitamin B12 are considered. For citation: Erina A.A., Borodulin V.B., Dereven’kov I.A., Makarov S.V., Ischenko A.A. Destruction of vitamin B12 during interaction with active oxygen species. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 7. P. 6-18. DOI: 10.6060/ivkkt.20246707.7043.

In this work, the morphology of zirconia, alumina, and silicas was studied, and static sorption of the repellents N, N-diethyl-3-methylbenzamide and ethyl-3-[acetyl(butyl)amino]propionate on these oxides was carried out. ZrO2, Al2O3, and SiO2 phenyl were shown to have high sorption activity to the repellents N, N-diethyl-3-methylbenzamide (239 mg/g for SiO2 phenyl) and ethyl-3-[acetyl(butyl)amino]propionate (251 mg/g for ZrO2). Pointedly, it was found that despite having the largest pore volume and high specific surface area (compared to the other studied oxides), SiO2 C2 has a significantly inferior sorption capacity in respect to other oxides, in particular SiO2 phenyl, which can be explained by the presence of the phenyl group in the latter that has chemical affinity for repellent molecules. Obtained isotherms of SiO2 300 also confirm the low sorption activity towards N, N-diethyl-3-methylbenzamide. The sorption equilibrium for both repellents, in most cases, is described by the Langmuir monomolecular adsorption model. The obtained results suggest that the studied zirconia, alumina, and silica can be used as carrier components of repellents.

Electron-phonon coupling is an important energy transfer mechanism in solids after ultrafast laser excitation. In this study, we present an extreme ultraviolet (EUV) and infrared (IR) pump-probe photoemission experiment to investigate the electron-phonon coupling in nonequilibrium gold. The energy of IR-laser-emitted photoelectrons is shifted due to the EUV photoemission and oscillates with a ∼4THz frequency. Such oscillation is considered as the effective excitation of the longitudinal acoustic phonon mode in gold through the spectral-dependent electron-phonon coupling. Our study showcases the capability of time-resolved photoemission electron microscopy to monitor the non-equilibrium lattice vibrations with ultrahigh spatial and temporal resolution.

In the adhesion zone of etiolated pea seedling roots located at a distance of 5–15 mm from its apex, at 1 and 24 h after inoculation with the bacteria Rhizobium, the effects of exogenous 10–11 M indole-acetic acid (IAA) and 10–9 M 6-benzylaminopurine (BAP) on cell metabolism were investigated. The inoculated seedlings were used as a control not exposed to the action of phytohormones. Phytohormone-induced changes in the activity of soluble and cell wall-related peroxidases (POs) and polyphenol oxidases (PPOs), the tissue concentrations of hydrogen peroxide (H2O2), and nitric oxide (NO), as well as “soluble” (extracted by ethyl acetate and n-butanol) and “insoluble” phenolic compounds (PCs) and flavonoids are discussed. The analysis of the results showed that during both observation periods the exogenous effect of the IAA enhanced the protective responses in the adhesion zone cells and the action of BAP weakened them. It was shown that the differences in the metabolism of adhesion zone cells resulting from the action of exogenous BAP and IAA were related to their diametrically opposite effects on nodulation.

The behavior of a thin-film GeTe crystal induced by intense femtosecond laser pulses ( λ = 0.8 1pt 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.

The possibility of amorphization of a thin germanium telluride crystal irradiated by high-power 800-nm femtosecond laser pulses has been investigated. The sample was a 20-nm-thick film of crystalline semiconductor GeTe. An electron diffractometer with a source of short photoelectron pulses was used to study the structural changes. The electron diffraction patterns were analyzed, and the α- and β- phases have been identified in GeTe. It is established that sample ablation occurs in the strong field of femtosecond laser pulses, which is accompanied by a decrease in the crystalline phase thickness to 5–6 nm without any significant amorphization of the sample. A specific feature of the observed process—the absence of light-induced transition of a thin GeTe film from the crystalline to the amorphous state under femtosecond laser irradiation—is noted. Possible causes of the revealed effect are discussed.

Objectives. The main aim of this review is to summarize the existing knowledge on the use of X-ray photoelectron spectroscopy (XPS) for the characterization of nanoparticles and nanomaterials.Results. XPS or electron spectroscopy for chemical analysis can provide information on the qualitative and quantitative composition, valence states of the elements of the samples under study, the chemical composition of the surface and interfaces that determine the properties of nanoparticles and nanostructured materials. The review describes the role of several different methods for the characterization of nanomaterials, highlights their advantages and limitations, and the possibilities of an effective combination. The main characteristics of XPS are described. Various examples of its use for the analysis of nanoparticles and nanomaterials are given in conjunction with additional methods to obtain complementary information about the object under study.Conclusions. XPS provides depth information comparable to the size of nanoparticles (up to 10 nm depth from the surface) and does not cause significant damage to the samples. Two disadvantages of XPS analysis are sample preparation requiring a dry solid form without contaminations and data interpretation. XPS provides information not only on the chemical identity, but also on the dielectric properties of nanomaterials, recording their charging/discharging behavior. Chemical information from the surface of nanoparticles analyzed by XPS can be used to estimate the thickness of nanoparticle coatings. XPS has a high selectivity, since the resolution of the method makes it possible to distinguish a characteristic set of lines in the photoelectron spectrum at kinetic energies determined by the photon energy and the corresponding binding energies in elements. The intensity of the lines depends on the concentration of the respective element. Obtaining a sufficiently complete picture of the properties of nanomaterials requires the use of a group of complementary instrumental methods of analysis.