Russian Journal of Physical Chemistry A最新文献

Thermodynamic properties of (CaO)_0.501(Al₂O₃)_0.098(SiO₂)_0.401 (Ca40.10) glass are studied using two techniques: low-temperature vacuum adiabatic calorimetry and high-temperature drop solution calorimetry. The enthalpy of formation from oxides (−17.6 ± 2.6 kJ/mol) is determined for the first time. Heat capacity is shown to grow monotonically with temperature in the interval of 8 to 357 K. No phase transitions are revealed in this region of temperatures. Results from measuring heat capacity are approximated using the semi-empirical Planck–Einstein model. The possibility of using incremental scheme to estimate the heat capacity of ternary glasses formed by calcium, aluminium, and silicon oxides is confirmed.

Gibbs energies of the transfer of cryptand[2.2.2] from water to a water–ethanol solvent of variable composition are determined from the interphase distribution of the substance between immiscible phases at a temperature of 298 K composition. It is established that the solvation of cryptand[2.2.2] weakens upon an increase in the concentration of alcohol in the solution. Literature data are used to calculate Gibbs energies of the transfer of protonated cryptand[2.2.2] and complexes of it with nickel(II) and copper(II) ions from water to water–ethanol mixtures.

An experiment is performed on introducing methane with a syringe at different helium flow rates on a chromatographic column free of adsorbent. It is found that the input signals generated in this case are satisfactorily described by an elution curve equation that is a correct solution to the direct problem of linear adsorption dynamics. A separate example shows that the input signals at the same flow rate coincide with one another quite well. The centers of gravity to the left and right of the input signal’s maximum are calculated, considerably expanding its content of information.

Results are presented from studying the permeability of Nafion-type perfluorinated sulfonic cation-exchange membranes used in membrane contact devices (MCDs) for chemical isotopic exchange between water and hydrogen. It is shown that the permeability of a perfluorinated sulfonic cation-exchange membrane grows after modifying it with Fe³⁺ ions and subsequent regeneration with a nitric acid solution. The best effect is observed for Nafion 212 membrane (50.8 µm), since its permeability is approximately tripled in the 298–343 K range of temperatures. It is shown that the state of a membrane has no effect on the observed energy of activation. Energy E_a = 14 ± 4 kJ/mol indicates that isotopic exchange is controlled by diffusion processes.

Protonated methane, ({text{CH}}_{5}^{ + }), has unusual vibrational and rotational behavior because its three nonequivalent equilibrium structures have nearly identical energies and its five protons scramble freely. The highly flexible ({text{CH}}_{5}^{ + }), molecular ion has been shown by ab initio calculations to have 120 symmetrically equivalent minima of Cs symmetry in its ground electronic state. Complete proton rearrangement, making all minima accessible to each other, is possible as a result of two large-amplitude internal motions: an internal rotation about the C₃ axis with an ab initio barrier of 30 cm^–1 and an internal flip motion with an ab initio barrier of 300 cm^–1 that exchanges protons between the H₂ and ({text{CH}}_{3}^{ + }) groups. We calculate the structure of the J = 2 ( leftarrow )1 and 1 ( leftarrow ) 0 rotational transitions of ({text{CH}}_{5}^{ + }), ({text{CD}}_{5}^{ + }) and also other variants containing ({text{C}}{{{text{H}}}_{x}}{text{D}}_{{(5 - x)}}^{ + }). Although many theoretical papers have been published on the quantum mechanics of these systems, a better understanding requires spectral and conformational analysis. Post Hartree-Fock, Møller-Plesset and DFT calculation with the correlation consistent polarized valence double and triple zeta basis sets have done for the zero-point energies of ({text{C}}{{{text{H}}}_{x}}{text{D}}_{{(5 - x)}}^{ + }). The present results indicates the mode 8, 12, and 10 agree with qualitative of ({text{CH}}_{5}^{ + }), which is highly fluxional and has a complex spectrum while the C–X bonds which are broken and reformed all the time. The spectrum of mode 12 is highly complex with huge red-and some blue shifts. In particular, they can be attributed to the rapid coupling of the original CH-stretching normal mode to motions more closely related to isomerization, i.e., bending or rocking. There has thus been a long debate whether ({text{CH}}_{5}^{ + }) has a structure at all or not and is it real rotational motions or artificial. In addition, we include the contribution to the torsional barrier from the zero point energies of the other (high-frequency) vibrations, the effect of centrifugal distortion, and the effect of second-order rotation-vibration interactions.

Molecular dynamics is used to calculate the vapor–liquid equilibrium and liquid–vapor surface tension for a methane–ethane system. Good agreement of the parachor value for ethane between the molecular model and experimental data is shown for the 203–253 K range of temperatures and pressures up to 60 atm. The dependence of the surface tension of the mixture on pressure in the range of 4–40 atm at a temperature of 213 K shows a drop in both the surface tension and the difference in densities between the liquid and vapor as the pressure rises and approaches the critical locus. Approximating the density profiles obtained for the same conditions, it is concluded that the width of the interphase boundary also grows. The amount of methane adsorbed on the surface of the liquid film is calculated. The dependence of the molar adsorption of methane on the difference between the densities of the components in the liquid and gas phases is obtained, along with its analytical expression in the context of the Gibbs theory. Features of the approach that is used include no need for approximations of the ideal gas or the ideal solution, and the use of only experimentally obtained data as input. The resulting values of methane adsorption are in good agreement with the derived analytical dependence.

Membranes have been prepared from polysulfone and graphene oxide with mass concentrations from 0 to 0.4%. A series of experiments were conducted to study the permeability of the obtained samples at pressures of 10, 15, and 20 atm. The experimental time dependences of the permeated water volume at a constant pressure were obtained. The dependence of the membrane permeability on the graphene oxide concentration and pressure was calculated. Conclusions were drawn about the influence of graphene oxide concentration and pressure on the permeability of the samples.

In this study, experimental carry out of liquid–vapor and solid–liquid phase transitions were conducted for the ternary system {CO₂ (1) + ethanol (2) + acetaminophen (3)} at different concentrations of paracetamol in ethanol for temperatures from 313 to 333 K and pressures up to 12 MPa. Experimental high pressure phase transition data were obtained using the static method in a variable volume view cell. Experimental data were compared with the literature for systems containing acetaminophen in a saturated solution. The presence of paracetamol in the binary system {CO₂ (1) + ethanol (2)} significantly alters the behavior of the phase under the conditions of temperature and concentration studied. It was observed that in the ternary system {CO₂ (1) + ethanol (2) + acetaminophen (3)} with a saturated solution at the lowest temperature, 313 K, CO₂ acts as a cosolvent for mole fractions lower than 0.6. Thermodynamic simulations employing the Perturbed Chain Statistical Associating Fluid Theory (PC-SAFT) Equations of State (EoS) aligned the experimental results adequately. The observed minimal deviations in pressure and temperature validate the efficacy of the thermodynamic models applied in this study.

The catalytic and adsorption properties of supported mono- and bimetallic nanoparticles of the copper–silver and copper–gold systems were studied. The particle sizes were 5–9 nm. The catalytic properties of the samples were studied at 77 K in deuterium–hydrogen exchange reactions and ortho-to-para conversion of protium. A comparison of the obtained data on the catalytic properties of the samples in isotope exchange reactions in molecular hydrogen and ortho-to-para conversion of protium showed that the mono- and bimetallic nanoparticles of the systems have magnetic properties. A comparison of the activities of the mono- and bimetallic systems in the deuterium–hydrogen exchange reaction revealed a more significant synergistic effect for the copper–gold system relative to the copper–silver system, which is explained by the greater difference between the electronegativities of atoms in the systems.