CASCADE OF AUGER TRANSITIONS IN SPECTRUM OF XENON: THEORETICAL DATA

The energy parameters of the Auger transitions for the xenon atomic system are calculated within the combined relativistic energy approach and relativistic many-body perturbation theory with the zeroth order density functional approximation. The results are compared with reported experimental data as well as with those obtained by semiempirical method. The important point is linked with an accurate accounting for the complex exchange-correlation (polarization) effect contributions and using the optimized one-quasiparticle representation in the relativistic many-body perturbation theory zeroth order that significantly provides a physically reasonable agreement between theory and experiment.

ON ESTIMATION OF THE AREA PER A SURFACTANT MOLECULE IN A 2D MONOLAYER DURING THE LIQUID-EXPANDED-LIQUID-CONDENSED PHASE TRANSITION AT THE AIR/WATER INTERFACE

Предложен метод оценки площади A, приходящейся на молекулу монослоя ПАВ, вначале перехода от жидко-растянутой к жидко-конденсированной фазе на основе двух теоретических моделей. Термодинамическая модель поведения дифильных монослоев с учетом неидеальности энтропии смешения позволяет оценить величину энергий Гиббса кластеризации ПАВ на основе П-А-изотерм, полученных при различных температурах. С другой стороны квантово-химический подход также дает возможность рассчитать данный термодинамический параметр и оценить структурные особенности получаемых монослоев. Величины энергий Гиббса кластеризации малых ассоциатов ПАВ и геометрических параметров элементарных ячеек монослоев были рассчитаны ранее с помощью квантово-химического полуэмпирического метода РМ3 для восьми классов дифильных соединений: насыщенные и этоксилированные спирты, насыщенные и цис-моноеновые карбоновые кислоты, α -гидрокси- и α -аминокислоты, N -ацилпроизводные аланина и диалкилзамещенные меламина. Эти параметры были использованы в термодинамической модели с учетом неидеальности энтропии смешения для расчета величин A. Оцененные значения A адекватно отражают экспериментальную температурную зависимость для рассматриваемого фазового перехода: с ростом температуры площадь, приходящаяся на молекулу ПАВ фиксированной длины цепи, уменьшается, и, наоборот, с ростом длины цепи ПАВ при фиксированной температуре величина A увеличивается. Это позволяет использовать предложенный подход в прогностических целях. A method is proposed to estimate the area per molecule of a surfactant monolayer A at the transition onset of the liquid-expanded to a liquid-condensed phase based on two theoretical models. A thermodynamic model with account for nonideality of the mixing entropy makes it possible to estimate the Gibbs energy of surfactant clusterization using the П-A isotherms obtained at different temperatures. On the other hand, the quantum-chemical approach also makes it possible to calculate this thermodynamic parameter and assess the structural features of the obtained monolayers. The values of the Gibbs clusterization energies of small surfactant associates and the geometric parameters of the monolayer unit cells were previously calculated using the quantum-chemical semiempirical method PM3 for eight classes of amphiphilic compounds: saturated and ethoxylated alcohols, saturated and cis-monoenic carboxylic acids, α-hydroxylic and α-amino acids, N -acyl-substituted alanines and dialkyl-substituted melamine. These parameters are used in the thermodynamic model with account for nonideality of the mixing entropy to calculate A. The estimated values Aadequately reflect the experimental temperature dependence for the considered phase transition: with an increase in temperature the area per surfactant molecule of a fixed chain length decreases, and vice versa, with an increase in the surfactant chain length at a fixed temperature, the value A increases. This makes it possible to use the proposed approach for prognostic purposes.

The Hydrodynamic Coefficient Analysis and Motion Control of the Lingyun Moveable Lander

A moveable lander has the advantages of low cost and strong controllability and is gradually becoming an effective autonomous ocean observation platform. In this study, the hydrodynamic property of the Lingyun moveable lander, which has completed experiments in the Mariana Trench in 2020, is analyzed with the semiempirical method and computational fluid dynamic (CFD) method. We calculate the inertial hydrodynamic coefficients and viscous hydrodynamic coefficients of the lander. The results show that the CFD can provide the hydrodynamic property for the moveable lander’s design. The dynamic equations and kinematic equations are completely constructed combined with the hydrodynamic coefficients. Subsequently, this paper utilized the PID control method and S control method to control the motions of the lander. The simulation results show that the methods accurately follow the preplanned path.

Semiempirical method for examining asynchronicity in metal–oxido-mediated C–H bond activation

The oxidation of substrates via the cleavage of thermodynamically strong C–H bonds is an essential part of mammalian metabolism. These reactions are predominantly carried out by enzymes that produce high-valent metal–oxido species, which are directly responsible for cleaving the C–H bonds. While much is known about the identity of these transient intermediates, the mechanistic factors that enable metal–oxido species to accomplish such difficult reactions are still incomplete. For synthetic metal–oxido species, C–H bond cleavage is often mechanistically described as synchronous, proton-coupled electron transfer (PCET). However, data have emerged that suggest that the basicity of the M–oxido unit is the key determinant in achieving enzymatic function, thus requiring alternative mechanisms whereby proton transfer (PT) has a more dominant role than electron transfer (ET). To bridge this knowledge gap, the reactivity of a monomeric MnIV–oxido complex with a series of external substrates was studied, resulting in a spread of over 104 in their second-order rate constants that tracked with the acidity of the C–H bonds. Mechanisms that included either synchronous PCET or rate-limiting PT, followed by ET, did not explain our results, which led to a proposed PCET mechanism with asynchronous transition states that are dominated by PT. To support this premise, we report a semiempirical free energy analysis that can predict the relative contributions of PT and ET for a given set of substrates. These findings underscore why the basicity of M–oxido units needs to be considered in C–H functionalization.

ON THE STARK BROADENING OF Ru III SPECTRAL LINES

Stark broadening parameters, full widths at half maximum (FWHM) and shifts for spectral lines within six multiplets of doubly charged ruthenium ions have been calculated, for an electron density of 1017 cm-3 and temperature range from 10 000 K to 160 000 K. Calculations have been performed with the simplified modified semiempirical (SMSE) approach. In the case of two multiplets, it is possible to apply the full modified semiempirical method. The corresponding calculations have been performed and results are compared in order to test and determine the accuracy of the SMSE approach. The results are also used for the consideration of Stark width and shift regularities in Ru III spectrum.

Chemical shift prediction of RNA imino groups: application toward characterizing RNA excited states

NH groups in proteins or nucleic acids are the most challenging target for chemical shift prediction. Here we show that the RNA base pair triplet motif dictates imino chemical shifts in its central base pair. A lookup table is established that links each type of base pair triplet to experimental chemical shifts of the central base pair, and can be used to predict imino chemical shifts of RNAs to remarkable accuracy. Strikingly, the semiempirical method can well interpret the variations of chemical shifts for different base pair triplets, and is even applicable to non-canonical motifs. This finding opens an avenue for predicting chemical shifts of more complicated RNA motifs. Furthermore, we combine the imino chemical shift prediction with NMR relaxation dispersion experiments targeting both 15N and 1HN of the imino group, and verify a previously characterized excited state of P5abc subdomain including an earlier speculated non-native G•G mismatch.

Stark Width Data for Tb II, Tb III and Tb IV Spectral Lines

A dataset of Stark widths for Tb II, Tb III and Tb IV is presented. To data obtained before, the results of new calculations for 62 Tb III lines from 5d to 6pj(6,j)o, a transition array, have been added. Calculations have been performed by using the simplified modified semiempirical method for temperatures from 5000 to 80,000 K for an electron density of 1017 cm−3. The results were also used to discuss the regularities within multiplets and a supermultiplet.

Comparison of theoretical and experimental investigation of protonation process of some thiones in acid media

PM3 semiempirical method was used for quantum chemical investigation in order to investigate the electronic properties and to determine the protonation centre in 1,2,4-triazoline-3-thione molecule. Confirmation of protonation center in acid media of investigated compounds was made using the values of atomic charges, as well as, proton affinity values. The results from semiempirical calculations indicated that the protonation center in the thione molecule was the sulphur atom. The behavior of thiones was investigated in mineral acid media using UV spectroscopy. The influence of the strength of the acid and its anion on the protonation process was discussed using three different mineral acids (perchloric, hydrochloric and phosphoric acid) for protonation. The protonation process in perchloric and hydrochloric acid took place in one step, while in phosphoric acid was not finished even when its concentration was to the highest degree. The dissociation constants of protonated forms (pKBH + ) and the solvation parameter m* values were calculated in accordance with "excess acidity" function method (Cox and Yates) using the absorbance data from the experimental and reconstructed spectra (Characteristic Vector Analysis (CVA)). The determined pKBH + values in hydrochloric acid had more negative value than those obtained in perchloric acid media. The pKBH + values were in agreement with the literature data for this class of compounds.