V. N. Chukanov

Dielectric characteristics of O2(H2O)i and (O2)2(H2O)i clusters. Computer-aided experiment

Absorption of oxygen molecules by water clusters with sizes of 10 ≤ i ≤ 50 is studied by the molecular dynamics method using the modified TIP4P model. It is revealed that the total dipole moment of the clusters nonmonotonically increases with their sizes. Absorption of O2 molecules tends to raise the static permittivity of the ultradispersed medium formed by the clusters. The real and imaginary parts of the permittivity of water clusters with absorbed O2 molecules are aperiodic functions of frequency. The permittivity components turn out to be nonmonotonic functions of cluster sizes. The IR absorption and reflectance spectra are calculated for clusters of pure water and aggregates with absorbed O2 molecules. After the addition of oxygen molecules, the absorption coefficient of the clusters decreases, while the reflection coefficient increases. It is concluded that the capture of oxygen molecules by atmospheric moisture may reduce the greenhouse effect.

Computer-aided study of oxygen absorption by water clusters. IR spectra of heteroclusters

Spectral characteristics of (H2O)n, (O2)m(H2O)n, and (O)i(H2O)n cluster systems, where m≤2, i≤4, and 10 ≤ n ≤ 50, are studied with the molecular dynamics method using a flexible molecule model. The IR absorption spectra are changed substantially as a result of O2 molecule dissociation, and in the presence of atomic oxygen in the clusters, the spectra are characterized by a deep minimum at 520 cm−1. The absorption of oxygen causes a marked reduction in reflection coefficient R of monochromatic IR radiation. The number of peaks in the R(ω) spectra decreases to two in the case of molecular oxygen absorption and is no larger than four in the case of atomic oxygen absorption. The absorption of atomic oxygen by the clusters is also accompanied by a significant increase in the dissipation of energy accumulated by the clusters. This effect weakens when molecular oxygen is absorbed. An increase in atomic oxygen concentration in the clusters renders their radiation harder.

PHYSICOCHEMICAL PROPERTIES OF WATER CLUSTERS IN THE PRESENCE OF HCl AND HF MOLECULES. MOLECULAR DYNAMIC SIMULATION

The molecular dynamic method is used to study the physicochemical properties of water clusters containing HCl and HF molecules. These impurity molecules have the ability to undergo hydration in water vapor. In clusters with the same number of water molecules, large dipole moments are induced for HCl, and smaller ones, for HF. The diffusion coefficient of the impurity in the clusters is slightly lower than the analogous characteristic for water molecules and exhibits nonmonotonous behavior with increasing size of the aggregate.

Simulation of dielectric properties and stability of clusters (H2O) i , CO2(H2O) i , and CH4(H2O) i

Molecular dynamics method is used for studying complex permittivity ɛ and the stability of individual water clusters as a function of the number of involved molecules (7 ≤ i ≤ 20) and also the corresponding characteristics of water aggregates with a captured CO2 or CH4 molecule. Absorption of the latter molecules leads to considerable changes in dielectric properties and stability of clusters. In particular, upon the addition of a CO2 molecule to a water cluster, the oscillation parameters of the real and imaginary parts of the permittivity change. Capture of a CH4 molecule by a water aggregate changes the ɛ(ω) dependence from the relaxation to resonance type. For i ≥ 15, the thermal stability of individual water clusters can be lower than that of aggregates CO2(H2O)i and CH4(H2O)i. The mechanical stability of (H2O)i ≥ 13 clusters can exceed that of heteroclusters under consideration. Clusters (H2O)i and CO2(H2O)i have approximately the same dielectric stability, whereas aggregates CH4(H2O)i exhibit lower stability with respect to electric perturbations.

The absorption of carbon and nitrogen monoxides by ultradisperse aqueous system: Computer experiment

The method of molecular dynamics is used to investigate the effect of absorption of carbon and nitrogen monoxides on the spectral characteristics of a disperse aqueous system. The absorption of CO molecules causes the reduction of the real and imaginary parts of permittivity, and the absorption of NO molecules results in smoothing out of the frequency dependence of these characteristics, which corresponds to that of a system of clusters of pure water. The integral absorptance and reflectance of IR radiation decrease after the attachment of CO molecules to water clusters and undergo insignificant changes as a result of absorption of NO molecules. An increase is observed in the integral power of emission of infrared radiation by disperse aqueous systems which absorbed CO or NO molecules. The clustering of water vapor causes an abrupt reduction of the number of scattering centers and the anti-greenhouse effect.

Hydration of N2 and Cl2 Molecules

The behavior of N2 and Cl2 molecules in H2O clusters was studied by the molecular dynamics method. Structural, thermodynamic, kinetic, and electrical properties of water aggregates containing N2 and Cl2 molecules were examined. The energy of the admixture-water interaction is negative and decreases as the cluster size increases. The electrostatic potential and the field strength undergo strong changes in the vicinity of aggregate border. The effect of hydration on the rate of some atmospheric reactions was considered.

Application of Molecular Dynamic Simulation of Water Clusters with CO and CO2 Molecules to Binary Nucleation Problems

The thermodynamic properties of pure water clusters and aqueous aggregates with either CO or CO2 molecule were calculated by the molecular dynamics method. The resulting size dependence of the surface tension of the clusters was used to determine the size of the critical seeds. The rate of homogeneous and binary nucleation in atmospheric air was estimated. The role of polar and nonpolar impurity molecules at the initial stage of steam condensation is discussed.

The Structure and Energetics of HF(H2O) n and HCl(H2O) n Clusters

The Voronoi polyhedrons constructed within the framework of molecular–dynamic model of water clusters are used for the analysis of the hydration of HF and HCl molecules. The metric (lengths, angles, surfaces, and volumes) and polyhedron energy parameters are considered. The quantitative characteristics of hydration are derived on this basis.