Spectral characteristics of water clusters in the presence of nitrogen dioxide

The absorption of NO₂ molecules by a water cluster containing 25 molecules was studied by molecular dynamics. The calculated dielectric characteristics of a system of (NO₂) _i (H₂O)₂₅ clusters (1 ≤ i ≤ 6) were compared with similar data for a cluster system of pure water. The ability of the disperse water system that trapped NO₂ molecules to absorb IR radiation increased, and the rate of the absorbed energy emission decreased. The Raman spectrum of the disperse system that absorbed NO₂ molecules changed most significantly in the low-frequency range. The emission time of cluster-generated radiation was much smaller than the lifetime of the clusters.     

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. Original Russian Text ? A.E. Galashev, V.N. Chukanov, O.A. Galasheva, 2006, published in Kolloidnyi Zhurnal, 2006, Vol. 68, No. 2, pp. 155–160.     

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. Original Russian Text ? A.E. Galashev, V.N. Chukanov, A.N. Novruzov, O.A. Novruzova, 2007, published in Elektrokhimiya, 2007, Vol. 43, No. 2, pp. 143–153.     

Spectral characteristics of water clusters in the presence of nitrate ions

Nitrate ion adsorption by water clusters is studied using the molecular dynamics method combined with a polarizable model of flexible molecules. It is established that successive addition of one to six NO ₃ ^? ions to an (H₂O)₅₀ cluster decreases the averaged electrical potential related to the center of masses of water molecules. The (H₂O)₅₀ cluster retains its thermodynamic stability, provided that no more than three nitrate ions are added to it. After NO ₃ ^? ions are adsorbed, the real and imaginary components of the dielectric permittivity and the intensity of the Raman spectrum decrease, while the intensity of the IR absorption spectrum increases. Moreover, ion adsorption by the water cluster reduces the IR absorption coefficient and refractive index.     

Molecular dynamics calculation of spectral characteristics of water clusters in the presence of ozone molecules and chlorine ions

Simultaneous interaction of the (H₂O)₅₀ cluster with O₃ molecules and Cl⁻ ions was studied by the molecular dynamics method. Six O₃ molecules located near the cluster were absorbed by the aqueous aggregate, and Cl⁻ ions in turn left the zone of the interaction with the cluster. Some of Cl⁻ ions penetrated inside the formed (O₃)₆(H₂O)₅₀ cluster and come into collision with O₃ molecules that split the ozone molecule into atoms. When Cl⁻ ions were removed sufficiently far away from the cluster, the water cluster with absorbed O₃ molecules and O atoms was observed for 15.6 ps. The interaction of water molecules with Cl⁻ ions gives rise to an increase in the integral intensity of absorption and emission IR spectra, and also to an essential decrease in the analogous characteristics of the Raman spectrum in the frequency range of 0 ≤ ω ≤ 1000 cm⁻¹. The presence of Cl⁻ ions did not affect essentially the location of the main band in the IR spectra, but considerably changed the shape of the bands in the Raman spectrum.     

Calculation of spectral characteristics of water clusters upon interaction with oxygen molecules and bromine ions

Interactions of (Br⁻) _i (H₂O)_50−i clusters (0 ≤ i ≤ 6) with molecular oxygen is studied by the molecular dynamics method using flexible molecule model. Values of real and imaginary parts of permittivity decrease in the 0 ≤ ω ≤ 3500 cm⁻¹ frequency range with increasing number of bromine ions in a cluster. The ability of cluster to absorb IR radiation decreases, whereas the reflectance and Raman light scattering remains nearly unchanged. An increase in the content of Br⁻ ions in the cluster lowers the power of emitted IR radiation and decreases the amount of active electrons participating in the interaction with IR radiation. However, when the concentration of Brions becomes substantially higher (at i = 5 and 6), the values of emitted power and the number of active electrons are restored to the values that are typical for water cluster in the absence of Br⁻ ions. At i ≥ 3, repelling Br⁻ ions acquire kinetic energy, which is sufficient to remove molecular oxygen from the system.     

Spectral effects of the clusterization of greenhouse gases: Computer experiment

Autocorrelation functions of the total dipole moment of clusters composed of H₂O and N₂O molecules are calculated in terms of the molecular dynamics method. The IR absorption and reflection spectra of systems composed of (H₂O)_i, N₂O(H₂O)_i, and (N₂O)₂(H₂O)_i clusters (2 ≤ i ≤ 20) are obtained on the basis of these functions. Frequency-dependent dielectric permittivity of clusters increases after the absorption of N₂O molecules. The absorption coefficient of cluster systems with trapped N₂O molecules increases at low frequencies and decays at frequencies ω > 500 cm^?1. The inclusion of N₂O molecules increases also reflection coefficient R and changes the pattern of R(ω) spectra. The absorption of IR radiation increases with the number of H₂O molecules in clusters. Dielectric losses also increase with an increase in i number upon the absorption of N₂O molecules. The number of electrons interacting with an incident electromagnetic wave increases upon the capture of N₂O molecules.     

Spectral characteristics of aqueous dispersions enriched in oxygen

The IR absorption and reflection spectra of aqueous dispersions consisting of (H₂O)_n, O₂(H₂O)_n, and (O₂)₂(H₂O)_n clusters (10 ≤ n ≤ 50) were calculated by the method of molecular dynamics using a flexible model of molecules. The frequency distribution of the power scattered by the cluster systems was obtained in the range 0 ≤ ω ≤ 3000 cm^?1. The capture of one oxygen molecule by the clusters is accompanied by a decrease in the absorption of the low-frequency IR radiation and by a peak of the absorption intensity in the vicinity of ω 2704 cm^?1. This is also accompanied by a decrease in the reflection coefficient throughout the frequency range and a decrease in the emission power at ω < 1030 and ω > 1700 cm^?1. Addition of two oxygen molecules to the clusters decreases the capability of the dispersions for the absorption, reflection, and scattering of IR radiation.     

IR absorption,reflection, and emission spectra of aqueous disperse systems interacting with nitric oxide

IR absorption, reflection, and emission spectra of aqueous disperse systems that absorbed molecules of nitric oxide are calculated. In order to reveal the effect of the absorption of NO molecules on the dielectric properties of water clusters with different sizes, clusters are divided into two groups. The first group consists of clusters containing two to ten water molecules, while the second group contains from 11 to 20 H₂O molecules. Six systems of clusters are studied, e.g., (H₂O) _n , and (NO)₂(H₂O) _n with 2 ≤ n ≤ 10 and 11 ≤ n ≤ 20 ranges. An increase in the cluster size in each group leads to the amplification of absorption, reflection, and the power of emission of IR radiation. The doubling of the NO concentration in the disperse system results in weak changes in the absorption of IR radiation, reduces the reflection and decreases the number of electrons participating in the interaction with external IR radiation, as well as significantly lowers the power of thermal radiation emitted by the system.     

Dielectric properties of water clusters containing CO and NO molecules. Computational experiment

The absorption of CO and NO molecules by (H₂O)₂₀ clusters was studied by the method of molecular dynamics. In general, the clusters containing CO molecules are more stable mechanically, while the clusters with NO molecules are more stable against heating. The mobility of NO molecules in such clusters is higher than that of CO molecules. The total dipole moment, the static dielectric permeability, the number of active electrons in the clusters, and the specific number of hydrogen bonds between water molecules possess peak values when the number of doping molecules i = 6. IR absorption spectra mostly acquire a smooth shape at i > 6. Capture of CO and NO molecules by water cluster operates as anti-greenhouse effect.     

IR absorption and Raman spectra of silicon dioxide nanoparticles in the presence of water: Computer experiment

Interactions of (SiO₂)₅₀ clusters with 10, 20, 30, or 40 water molecules are studied by molecular dynamics method. Flat SiO₂ nanoparticle covered with a water layer is formed after the inclusion of water molecules into the cluster. As a rule, the integral intensity of IR and Raman spectra lowers after the absorption of H₂O molecules by the cluster. The power of IR radiation emitted by the cluster increases nonmonotonically with the addition of water molecules to the cluster. The absorption of water molecules by the cluster leads to a significant increase in the absorption coefficient and only a slight increase in the refractive index. The number of electrons participating in the interaction with electromagnetic radiation increases with the addition of water molecules to the cluster.     

Computer study of the absorption of ethane by aqueous ultradispersed medium: IR spectra

Absorption of ethane molecules by water clusters containing 10–20 molecules is studied by the molecular dynamics method. The (H₂O) _n (I), C₂H₆(H₂O) _n (II), and (C₂H₆)₂(H₂O) _n (III) cluster systems are composed on the basis of specific statistical weights. Spectral characteristics of system and single clusters are determined in the frequency range of 0 ≤ ω ≤ 1000 cm^?1. In this frequency range, both real and imaginary parts of dielectric permittivity decrease monotonically after the absorption of C₂H₆ molecules by an aqueous ultradispersed system. Integral coefficient of IR absorption increases, while average (over frequency) reflection coefficient decreases after the absorption of ethane molecules. The intensity of IR scattering by the systems of clusters containing C₂H₆ molecules lowers. Maximal values of radiation power for water clusters with various sizes are balanced with the capture of ethane molecules by the clusters, whereas oscillations in the size dependence of the density of electrons that are active with respect to IR radiation decrease.     

Computer Simulation of the Absorption of CO<Subscript>2</Subscript> Molecules by Water Cluster: 3. Dynamic and Dielectric Properties

Autocorrelation functions of translational and angular velocities of H₂O and CO₂ molecules in (CO₂)_i(H₂O)₁₀ clusters that are generated by the molecular dynamics method, as well as their frequency spectra, are calculated. Self-diffusion coefficients of molecules in clusters are determined. The IR spectra thus obtained and frequency-dependent dielectric permittivity of the clusters indicate the enhancement of absorption of Earth’ thermal radiation by these aggregates with an increase in the number of CO₂ molecules in the aggregates. Dielectric losses also increase with the i number.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 3, 2005, pp. 322–327.Original Russian Text Copyright © 2005 by Galashev, Rakhmanova, Chukanov.     

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.     

Dehydration-induced changes in the vibrational states of dioptase Cu6Si6O18·6H2O

This paper reports on the results of temperature studies (20–880°C) of the IR absorption spectra of dioptase crystals in the range 50–4000 cm⁻¹. During the dehydration of dioptase the state of water changes as follows: (1) initial state, (2) intermediate state with damped external vibrations of H₂O, (3) isolated water molecules with new hydrogen bonds, (4) formation of hydroxyls. The bands of the external virations of H₂O (1) vanish in state (2) because of the formation of vacancies in the six-membered water rings. The frequencies of the translation vibrations of 6H₂O in initial dioptase are close to those in liquid water: 169–170 and 277–290 cm⁻¹. A factor-group analysis of the dioptase vibrations in the space group C _3i ² is performed. All IR active vibrations 23A_u+23E_u are described. The thirty five bands observed in the IR spectra are assigned. The dehydration-induced deformations of the silicate rings are determined from the shifts of the vibrational bands of Si₆O₁₈. Institute of Mineralogy and Petrography, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 1, pp. 68–74, January–February, 1996. Translated by I. Izvekova     

Computer Simulation of the Absorption of CO<Subscript>2</Subscript> Molecules by Water Cluster: 1. The Stability

The (CO₂)_i(H₂O)₁₀ clusters with the kinetic energy corresponding to a temperature of 233 K is simulated by the molecular dynamics method. The stability of these clusters with respect to thermal, mechanical, and dielectric perturbations, as well as to the absorption of CO₂ molecules, is studied. It is shown that the cluster composed of 10 water molecules remains thermodynamically stable if it captures one or two CO₂ molecules. Clusters are absolutely unstable when 3 ≤ i ≤ 9. A metastable state of clusters is achieved at i > 9.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 3, 2005, pp. 308–314.Original Russian Text Copyright © 2005 by Galashev, Rakhmanova, Chukanov.     

Computer Simulation of the Absorption of CO<Subscript>2</Subscript> Molecules by Water Cluster: 2. The Microstructure

The simulation of the absorption of CO₂ molecules by the (H₂O)₁₀ cluster is performed by the molecular dynamics method using the modified TIP4P model of water. The detailed structure of (CO₂)_i(H₂O)₁₀ clusters (0≤i≤11) is analyzed by the statistic geometry method based on the construction of the Voronoi polyhedra. The obtained distributions of the geometric elements of polyhedra indicate the significant changes in the structure of a cluster after the absorption of one CO₂ molecule. Only polyhedra characterizing the structure of unstable water clusters that absorbed six or seven CO₂ molecules demonstrate a nonsphericity close to the ideal tetrahedron. Linear CO₂ molecule tends to be oriented in a cluster so that the average angle formed by this molecule and permanent dipole moments of water molecules would be equal to about 30°.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 3, 2005, pp. 315–321.Original Russian Text Copyright © 2005 by Galashev, Rakhmanova, Chukanov.     

Cluster mechanism of the atmosphere ozone destruction by bromine ions

Interaction of bromine ions absorbed by water cluster with adsorbed oxygen and ozone molecules has been investigated by the molecular dynamics method. It was shown that the part of O₂ molecules was removed from the system by evaporating Br⁻ ions, while all O₃ molecules and Br ions were kept in the system during 25 ps. The increase the concentration of the Br⁻ ions in the clusters resulted in a reduction of the absorption intensity and emission in IR spectra at the presence of oxygen, whereas the absorption intensity in the appropriate IR spectra of ozone-containing systems increased with the growth of a number of the Br⁻ ions. Raman spectra of oxygen-containing systems were poorly sensitive to the concentration of the Br⁻ ions but the absorption intensity of Raman spectra for systems with ozone considerably decreased with the growth of a number of bromine ions.     

Computer simulation of oxygen and nitrate ion absorption by water clusters

Using the molecular dynamics method, the joint absorption of oxygen and nitrate ions by water clusters is studied in terms of the polarizable model of flexible molecules. Significant fluctuations are observed in the number of hydrogen bonds in the clusters during the addition of NO₃⁻ ions to water-oxygen aggregates. Dielectric permittivity noticeably changes upon the addition of O₂ molecules to water clusters and nitrate ions to oxygen-containing water clusters. After the absorption of oxygen molecules and nitrate ions, water clusters markedly lose the ability to IR absorption. The Raman spectrum of a medium formed from disperse aqueous system, oxygen, and nitrate ions displays a greater number of bands than the spectrum of a system of pure water clusters.     

Spectral characteristics of water clusters upon interaction with oxygen molecules and chlorine ions

The interactions of a 6O₂ + (H₂O)₅₀ system with two, four, or six Cl⁻ ions are studied by the molecular dynamics method. The integral intensity of IR and Raman spectra decreases with an increase in the number of Cl⁻ ions surrounding the system. The values of real and imaginary parts of dielectric permittivity increase with the rise in the frequency reaching maxima in the 850 ≤ ω ≤ 950 cm⁻¹. As a result of interactions between ions and the formed (O₂)₆ (H₂O)₅₀ cluster, the pattern of the reflection spectrum of IR radiation becomes smoother. The interaction between 6O₂ + (H₂O)₅₀ system and Cl⁻ ions leads to the substantial increase in the power of emitted radiation. With time, Cl⁻ ions gradually leave the interaction zone with the system. Maximum residence time of the last ion near the system boundary does not exceed 3 ps. Cl⁻ ions located closer to O₂ molecules do not penetrate into the depth of an (O₂)₆ (H₂O)₅₀ cluster.