Computer Simulation of Charge Separation in Vapor–Gas Mixtures

The interaction between counterions in water vapor is modeled by the Monte-Carlo method. A material contact of a system with vapor is modeled using a large canonical statistical ensemble. A powerful minimum, which forms in the medium-strength interaction potential at the expense of pulling molecules into the ion–ion gap, leads to separation of charges and stabilization of ions at distances that are much greater than the thickness of hydration shells of the ions. Spatial charge separation dramatically inhibits recombination and leads to accumulation of nonrecombined ion pairs. The discovered effect is of universal nature and explains some important atmospheric phenomena and results of electrometric laboratory experiments in moist air.     

Water vapor clustering in the field of a chlorine anion occurring in a planar nanopore with structureless walls

The Monte Carlo bicanonical statistical ensemble method has been employed to calculate the free energy, entropy, and work of Cl^? ion hydration in model planar pores 0.5 and 0.7 nm wide at 298 and 400 K. A detailed model of many-body interactions with the ion has been used, the model being matched to experimental data with respect to the free energy and enthalpy of attachment reaction in water vapor. Under the conditions of a restricted volume, the equilibrium size of a hydration shell substantially decreases, with the effect becoming stronger in the range of moderate and large sizes. In moderately supersaturated vapors, under the conditions of a nanopore, the ion loses its hydration shell as the temperature is decreased. In supersaturated vapors, the hydration shell formed on the ion is thermodynamically stable, while the stability crisis shifts to the region of larger sizes. The enhancement of the thermodynamic stability in the pore results from a rise in the chemical potential of molecules due to the deficiency of closet neighbors and a reduction in the entropy under the conditions of the restricted volume. As the temperature is elevated, the effect of ion displacement out of its hydration shell is leveled. The regularities derived in terms of the estimation model based on the capillary approximation are in qualitative agreement with the results of computer simulation.     

Molecular structure of finely disperse Na+Cl−(H2O) n aerosol particles in water vapor

The thermodynamic states corresponding to solvent separated (SSIP) and contacting (CIP) Na⁺Cl^? ion pairs in molecular water clusters have been obtained by random walks in a configurational space with an equilibrium distribution function at 273 and 150 K. The transition to the SSIP state begins in a thresh-old-type manner in clusters containing 10–12 molecules, with the interionic distance increasing continuously up to disintegration into two hydrated ions with the growth of a hydration shell. As the cluster size increases, the hydration shell shifts from sodium ion to chlorine ion. In the first hydration layer, the electric field of the ions ruptures as many as 50% of hydrogen bonds.     

Domain nucleation in the contact layer at an interface of water and a polarizable substrate

The growth of a molecular water film on the basic plane of a silver iodide monocrystal is studied through computer simulation. Decomposition into domains with spontaneous polarization is observed in the contact layer of the film at the interface with the substrate. The formation of domains is found to be sharply enhanced on a model substrate with the double polarizability of iodine ions; heteropolarization interactions caused by the formation of domain structures increase the film’s coupling with the substrate. It is demonstrated that the vapor pressure needed for molecular film growth is reduced appreciably via heteropolarization interactions.     

Spin of the ground quantum state of electrons from first principles in the representation of Feynman path integrals

A method for calculating the spin of the ground quantum state of nonrelativistic electrons and distance between energy levels of quantum states differing in the spin magnitude from first principles is proposed. The approach developed is free from the one-electron approximation and applicable in multielectron systems with allowance for all spatial correlations. The possibilities of the method are demonstrated by the example of calculating the energy gap between spin states in model ellipsoidal quantum dots with a harmonic confining field. The results of computations by the Monte Carlo method point to high sensitivity of the energy gap to the break of spherical symmetry of the quantum dot. For three electrons, the phenomenon of inversion has been revealed for levels corresponding to high and low values of the spin. The calculations demonstrate the practical possibility to obtain spin states with arbitrarily close energies by varying the shape of the quantum dot, which is a key condition for development prospects in technologies of storage systems based on spin qubits.     

Mechanisms for ion retention in molecular water clusters in a planar nanopore against the background of thermal fluctuations

The Monte Carlo method has been used to calculate the potential of mean force for Na⁺ and Cl^? ions interacting in model planar nanopores with structureless walls under the conditions of the material contact with water vapor at room temperature and above water boiling point. The interactions have been described using a detailed many-body model calibrated with respect to experimental data on the free energy of attachment reactions and the results of quantum-chemical calculations. Dissociation becomes possible when the vapor density increases as a sufficient number of molecules are pulled into the field of the ions. The dissociation proceeds sooner under the conditions of the nanopore than in bulk water vapor. Hydration decreases the energy of the dissociated state; however, the entropy component of the free energy partly compensates for the decrease in the internal energy, thereby increasing the stability of a contact ion pair. After the dissociation of a contact ion pair (CIP), ions are retained within a cluster in the state of a solvent-separated ion pair (SSIP). Fluctuations in the number of pulled-in vapor molecules, which are correlated with fluctuations in the interionic distance, stabilize the SSIP states with respect to recombination, while a decrease in the screening of the field of ions under the conditions of the nanopore stabilize the SSIP states with respect to cluster decay. The conditions of the nanopore stimulate the passage of an ion pair from the CIP to the SSIP state due to the rearrangement of the statistical weights in favor of molecules being located in the interionic gap. Thus, under the conditions of the nanopore, the stability of the SSIP states increases with respect to both the recombination of the ions and the decay of the ion-molecular associate.     

Multiphoton mass spectra of XeKr molecules in the range of excited Xe*6<Emphasis Type="Italic">p</Emphasis>[5/2]<Subscript>2, 3</Subscript> atoms

Data on excited states of XeKr molecules in the energy range 78280–77600 cm^?1 are obtained. Using the method of multiphoton laser photoionization of molecules in a supersonic jet, five vibrational progressions of XeKr molecules are obtained, which are attributed to five electronic-vibrational transitions from the ground state of the XeKr molecule of the symmetry 0⁺ to excited states of the symmetry Ω = 0⁺, 1, 2 with the dissociation limit Kr¹ S ₀ + Xe*6p[5/2]₂ and of the symmetry Ω = 1, 2 with the dissociation limit Kr + Xe*6 p [5/2]₃. The molecular constants of the corresponding excited states of the XeKr molecule are estimated.     

Thermal ionization in hydrogen plasma simulated using Feynman path integrals

Thermal ionization of hydrogen at temperatures on the order of 10⁴–10⁵ K and densities within 10²⁴–10²⁸ m^?3 has been simulated using Feynman path integrals. This method has been realized for the first time under conditions of a statistical ensemble with fluctuating volume. Multidimensional integrals have been calculated using the Monte Carlo simulation method that was preliminarily tested numerically on a problem of the quantum ground state of a confined hydrogen atom, which admits analytical solution. The position of isolines of the degree of ionization has been determined on the p-T plane of plasma states. The spatial correlation functions for electrons and nuclei are calculated, and the quantum effects in behavior of the electron component are evaluated. It is shown that, owing to the presence of strong Coulomb interactions, plasma retains a substantially quantum character in a broad domain of thermodynamic states, where a formal use of the degeneracy criterion predicts a classical regime. A basically exact stochastic method is developed for calculating the equilibrium kinetic energy of a spatially bounded system of quantum particles free of the dispersion divergence.