The Experts below are selected from a list of 105633 Experts worldwide ranked by ideXlab platform

Kurt V. Mikkelsen - One of the best experts on this subject based on the ideXlab platform.

  • benchmarking sampling methodology for calculations of rayleigh light scattering properties of atmospheric Molecular Clusters
    Physical Chemistry Chemical Physics, 2019
    Co-Authors: Teis Joranger, Jonas Elm, Jens Vive Kildgaard, Solvejg Jorgensen, Kurt V. Mikkelsen
    Abstract:

    We present four different computational methods for benchmarking the sampling and Rayleigh light scattering of atmospheric Molecular Clusters containing hydrogen bonds. For sampling the cluster configurational space we test both the semi-empirical PM6 and PM7 methods, as well as the density functional ωB97X-D with the 6-31G and 6-31++G(d,p) basis sets. As a model system we study Clusters consisting of one hydrogen peroxide molecule (H2O2) and 1–5 water molecules. Hydrogen peroxide is an important constituent in the atmosphere where it acts as an oxidant. We find that all the sampling methods show conformational dissimilarities for the studied (H2O2)(H2O)1–5 Clusters. Notably the results for the largest studied (H2O2)(H2O)5 cluster show that the sampling methods perform very differently in finding the same low Gibbs free energy conformers. We consider the magnitude of elastic Rayleigh light scattering of the Clusters and how the scattering depends on the number of water molecules in the Clusters. We observe that the final Boltzmann averaged Rayleigh scattering is independent of the sampling method and that the inexpensive semi-empirical methods can be applied without loss of accuracy. This implies that Rayleigh scattering is a robust property that does not depend significantly on cluster conformations, but instead mainly on the composition of the cluster.

  • Rayleigh light scattering properties of atmospheric Molecular Clusters consisting of sulfuric acid and bases
    Physical Chemistry Chemical Physics, 2015
    Co-Authors: Jonas Elm, Patrick Norman, Kurt V. Mikkelsen
    Abstract:

    The Rayleigh light scattering properties of (H2SO4)a(NH3)b and (H2SO4)a((CH3)2NH)b atmospheric Molecular Clusters have been investigated using a response theory approach. Using density functional theory the Molecular structures and stepwise formation free energies of Clusters with a and b up to 4 have been re-investigated. The Rayleigh scattering intensities are calculated from the dipole polarizability tensor α using the CAM-B3LYP functional by applying linear response methods. The intrinsic scattering properties of (H2SO4)a(NH3)b and (H2SO4)a((CH3)2NH)b indicate that amine containing Clusters scatter light significantly more efficiently then their ammonia containing counterparts. Using the Atmospheric Cluster Dynamics Code (ACDC) the steady state cluster concentrations are estimated and the effective scattering is calculated. The effective scattering is shown to be highly dependent on the estimated concentrations and indicates that there exist competitive pathways, such as nucleation and coagulation, which influence the cluster distributions. The frequency dependence of the scattering is found to depend on the cluster composition and show increased responses when Clusters contain more bases than acid molecules. Based on structures obtained using semi-empirical Molecular dynamics simulations the Rayleigh scattering properties of Clusters with up to 20 acid–base pairs are evaluated. This study represents the first step towards gaining a fundamental understanding of the scattering properties of small atmospheric Clusters in the ambient atmosphere.

Jonas Elm - One of the best experts on this subject based on the ideXlab platform.

  • Modeling the formation and growth of atmospheric Molecular Clusters: A review
    Journal of Aerosol Science, 2020
    Co-Authors: Jonas Elm, Jakub Kubečka, Vitus Besel, Theo Kurtén, Matias J. Jääskeläinen, Roope Halonen, Hanna Vehkamäki
    Abstract:

    Abstract Molecular Clusters are ubiquitous constituents of the ambient atmosphere, that can grow into larger sizes forming new aerosol particles. The formation and growth of small Clusters into aerosol particles remain one of the largest uncertainties in global climate predictions. This has made the modelling of atmospheric Molecular clustering into an active field of research, yielding direct Molecular level information about the formation mechanism. We review the present state-of-the-art quantum chemical methods and cluster distribution dynamics models that are applied to study the formation and growth of atmospheric Molecular Clusters. We outline the current challenges in applying theoretical methods and the future directions to move the field forward.

  • benchmarking sampling methodology for calculations of rayleigh light scattering properties of atmospheric Molecular Clusters
    Physical Chemistry Chemical Physics, 2019
    Co-Authors: Teis Joranger, Jonas Elm, Jens Vive Kildgaard, Solvejg Jorgensen, Kurt V. Mikkelsen
    Abstract:

    We present four different computational methods for benchmarking the sampling and Rayleigh light scattering of atmospheric Molecular Clusters containing hydrogen bonds. For sampling the cluster configurational space we test both the semi-empirical PM6 and PM7 methods, as well as the density functional ωB97X-D with the 6-31G and 6-31++G(d,p) basis sets. As a model system we study Clusters consisting of one hydrogen peroxide molecule (H2O2) and 1–5 water molecules. Hydrogen peroxide is an important constituent in the atmosphere where it acts as an oxidant. We find that all the sampling methods show conformational dissimilarities for the studied (H2O2)(H2O)1–5 Clusters. Notably the results for the largest studied (H2O2)(H2O)5 cluster show that the sampling methods perform very differently in finding the same low Gibbs free energy conformers. We consider the magnitude of elastic Rayleigh light scattering of the Clusters and how the scattering depends on the number of water molecules in the Clusters. We observe that the final Boltzmann averaged Rayleigh scattering is independent of the sampling method and that the inexpensive semi-empirical methods can be applied without loss of accuracy. This implies that Rayleigh scattering is a robust property that does not depend significantly on cluster conformations, but instead mainly on the composition of the cluster.

  • Rayleigh light scattering properties of atmospheric Molecular Clusters consisting of sulfuric acid and bases
    Physical Chemistry Chemical Physics, 2015
    Co-Authors: Jonas Elm, Patrick Norman, Kurt V. Mikkelsen
    Abstract:

    The Rayleigh light scattering properties of (H2SO4)a(NH3)b and (H2SO4)a((CH3)2NH)b atmospheric Molecular Clusters have been investigated using a response theory approach. Using density functional theory the Molecular structures and stepwise formation free energies of Clusters with a and b up to 4 have been re-investigated. The Rayleigh scattering intensities are calculated from the dipole polarizability tensor α using the CAM-B3LYP functional by applying linear response methods. The intrinsic scattering properties of (H2SO4)a(NH3)b and (H2SO4)a((CH3)2NH)b indicate that amine containing Clusters scatter light significantly more efficiently then their ammonia containing counterparts. Using the Atmospheric Cluster Dynamics Code (ACDC) the steady state cluster concentrations are estimated and the effective scattering is calculated. The effective scattering is shown to be highly dependent on the estimated concentrations and indicates that there exist competitive pathways, such as nucleation and coagulation, which influence the cluster distributions. The frequency dependence of the scattering is found to depend on the cluster composition and show increased responses when Clusters contain more bases than acid molecules. Based on structures obtained using semi-empirical Molecular dynamics simulations the Rayleigh scattering properties of Clusters with up to 20 acid–base pairs are evaluated. This study represents the first step towards gaining a fundamental understanding of the scattering properties of small atmospheric Clusters in the ambient atmosphere.

Alexander I. Sidorov - One of the best experts on this subject based on the ideXlab platform.

  • The influence of sodium nanoparticles formation on luminescent properties of fluorophosphate glasses containing Molecular Clusters and quantum dots of lead selenide
    Optics and Spectroscopy, 2016
    Co-Authors: Zh. O. Lipatova, Elena Kolobkova, Alexander I. Sidorov, Nikolay Nikonorov
    Abstract:

    The influence of sodium nanoparticles and secondary heat treatment conditions on the spectralluminescent characteristics of fluorophosphate glasses with PbSe Molecular Clusters and quantum dots is studied. Experiments with glasses containing no sodium nanoparticles show that their thermal treatment leads to the formation of Molecular Clusters with subsequent formation of quantum dots having an intense luminescence. The results of numerical simulation for glasses with sodium nanoparticles shows that heat treatment leads to formation of a sodium fluoride shell on the nanoparticles surface. It is shown that quenching of the luminescence of PbSe Molecular Clusters and quantum dots takes place in these glasses.

  • Luminescent properties of Molecular Clusters (CdS)n in fluorophosphate glass
    Glass Physics and Chemistry, 2015
    Co-Authors: Elena Kolobkova, Nikolay Nikonorov, Alexander I. Sidorov, D. S. Kukushkin, T. A. Shakhverdov
    Abstract:

    It is shown experimentally that subnanodimensional Molecular Clusters (CdS)n are formed by synthesis in fluorophosphate glass containing cadmium and sulfur ions. They possess an intense luminescence in the visible region of the spectrum when being excited by UV radiation. Thermal treatment of such glass results in an increase in the size of the Molecular Clusters and makes their optical properties approach those of semiconductor CdS quantum dots. Luminescent fluorophosphate glass with (CdS)n Clusters can find applications in spectral down-converters of solar UV radiation in solar energetics, in light-emitting diodes of white radiation, and in luminescent detectors and sensors.

  • The effect of ions of rare-earth metals on the temperature dependence of the luminescence of Molecular Clusters of silver in oxyfluoride glasses
    Journal of Optical Technology, 2014
    Co-Authors: D. S. Arafonova, Elena Kolobkova, Alexander I. Sidorov, Nikolay Nikonorov
    Abstract:

    The influence of temperature on the spectral composition and luminescence intensity of oxyfluoride glasses containing Molecular Clusters of silver and ions of the rare-earth metals samarium and terbium has been investigated. It is shown that introducing these ions into the composition of the glass increases the luminescence intensity of the Molecular Clusters of silver and the temperature sensitivity of their luminescence intensity. In oxyfluoride glass with Molecular Clusters of silver and Tb3+ ions, the overall luminescence intensity in the 20°C–250°C temperature range is attenuated by a factor of 50. It is shown that Molecular Clusters of silver are characterized by temperature sensitivity of the luminescence intensity in the range 0.045–0.099  dB/°C.

  • Influence of halogenides on luminescence from silver Molecular Clusters in photothermorefractive glasses
    Technical Physics, 2014
    Co-Authors: Victor Dubrovin, Nikolay Nikonorov, A. I. Ignat’ev, Alexander I. Sidorov
    Abstract:

    It is shown experimentally that a rise in the sodium halogenide (NaCl, NaBr) concentration in photothermorefractive glasses increases the intensity of luminescence from silver neutral Molecular Clusters. Substitution of NaBr for NaCl with their concentration being the same shifts the luminescence band toward longer waves and raises its intensity. These findings can be explained by the formation of Molecular Clusters of type Ag n -Hal (Hal = Cl, Br) in photothermorefractive glass.

  • Luminescence of silver Molecular Clusters in photo-thermo-refractive glasses
    Optical Materials, 2014
    Co-Authors: Victor Dubrovin, A. I. Ignatiev, Nikolay Nikonorov, Alexander I. Sidorov, T. A. Shakhverdov, Darina S. Agafonova
    Abstract:

    abstract The luminescence spectra of silver Molecular Clusters in photo-thermo-refractive glasses are investigatedin detail before and after the UV irradiation and also after the heat treatment of the samples. In the initialphoto-thermo-refractive glass sample, silver is shown to occur in the form of Ag + ions and positivelycharged Molecular Clusters. After the UV irradiation with the wavelength corresponding to the Ce 3+ ionabsorption, these species are assumed to pass partially to the neutral state, thus forming the Ag 0 atomsand neutral Molecular Clusters such as Ag 2 ,Ag 3 , and Ag 4 that exhibit an intense luminescence in the vis-ible. A subsequent heat treatment at temperatures below the glass transition one results in an increase inthe intensity of the luminescence due to an increase in the concentration of neutral Molecular Clusters.Also investigated are the influence of halogens such as Cl and Br in glass matrix composition on the lumi-nescence of silver Molecular Clusters in photo-thermorefractive glasses and the effect of temperature onthe luminescence spectra of photo-thermorefractive glasses. 2013 Elsevier B.V. All rights reserved.

Darina S. Agafonova - One of the best experts on this subject based on the ideXlab platform.

  • Luminescence of silver Molecular Clusters in photo-thermo-refractive glasses
    Optical Materials, 2014
    Co-Authors: Victor Dubrovin, A. I. Ignatiev, Nikolay Nikonorov, Alexander I. Sidorov, T. A. Shakhverdov, Darina S. Agafonova
    Abstract:

    abstract The luminescence spectra of silver Molecular Clusters in photo-thermo-refractive glasses are investigatedin detail before and after the UV irradiation and also after the heat treatment of the samples. In the initialphoto-thermo-refractive glass sample, silver is shown to occur in the form of Ag + ions and positivelycharged Molecular Clusters. After the UV irradiation with the wavelength corresponding to the Ce 3+ ionabsorption, these species are assumed to pass partially to the neutral state, thus forming the Ag 0 atomsand neutral Molecular Clusters such as Ag 2 ,Ag 3 , and Ag 4 that exhibit an intense luminescence in the vis-ible. A subsequent heat treatment at temperatures below the glass transition one results in an increase inthe intensity of the luminescence due to an increase in the concentration of neutral Molecular Clusters.Also investigated are the influence of halogens such as Cl and Br in glass matrix composition on the lumi-nescence of silver Molecular Clusters in photo-thermorefractive glasses and the effect of temperature onthe luminescence spectra of photo-thermorefractive glasses. 2013 Elsevier B.V. All rights reserved.

  • The effect of temperature on the luminescence of Molecular Clusters of silver in photothermorefractive glasses
    Journal of Optical Technology, 2013
    Co-Authors: Darina S. Agafonova, A. I. Ignat’ev, V. I. Egorov, Alexander I. Sidorov
    Abstract:

    This paper presents the experimental results of a study of how temperature affects the luminescence of Molecular Clusters of silver in photothermorefractive glasses. It is shown that, after the glasses are UV-irradiated in the absorption band of cerium ions, intense and broad-band luminescence appears in the visible region. The luminescence centers responsible for this luminescence are neutral silver atoms and neutral Molecular Clusters of silver. Heat treatment at 350°C causes a tenfold increase of the luminescence intensity. The luminescence intensity decreases by a factor of 10 as the sample’s temperature is increased from 25°C to 200°C. The temperature dependence of the normalized luminescence intensity is shown for a fiber with silver introduced by ion exchange.

Victor Dubrovin - One of the best experts on this subject based on the ideXlab platform.

  • Influence of halogenides on luminescence from silver Molecular Clusters in photothermorefractive glasses
    Technical Physics, 2014
    Co-Authors: Victor Dubrovin, Nikolay Nikonorov, A. I. Ignat’ev, Alexander I. Sidorov
    Abstract:

    It is shown experimentally that a rise in the sodium halogenide (NaCl, NaBr) concentration in photothermorefractive glasses increases the intensity of luminescence from silver neutral Molecular Clusters. Substitution of NaBr for NaCl with their concentration being the same shifts the luminescence band toward longer waves and raises its intensity. These findings can be explained by the formation of Molecular Clusters of type Ag n -Hal (Hal = Cl, Br) in photothermorefractive glass.

  • Luminescence of silver Molecular Clusters in photo-thermo-refractive glasses
    Optical Materials, 2014
    Co-Authors: Victor Dubrovin, A. I. Ignatiev, Nikolay Nikonorov, Alexander I. Sidorov, T. A. Shakhverdov, Darina S. Agafonova
    Abstract:

    abstract The luminescence spectra of silver Molecular Clusters in photo-thermo-refractive glasses are investigatedin detail before and after the UV irradiation and also after the heat treatment of the samples. In the initialphoto-thermo-refractive glass sample, silver is shown to occur in the form of Ag + ions and positivelycharged Molecular Clusters. After the UV irradiation with the wavelength corresponding to the Ce 3+ ionabsorption, these species are assumed to pass partially to the neutral state, thus forming the Ag 0 atomsand neutral Molecular Clusters such as Ag 2 ,Ag 3 , and Ag 4 that exhibit an intense luminescence in the vis-ible. A subsequent heat treatment at temperatures below the glass transition one results in an increase inthe intensity of the luminescence due to an increase in the concentration of neutral Molecular Clusters.Also investigated are the influence of halogens such as Cl and Br in glass matrix composition on the lumi-nescence of silver Molecular Clusters in photo-thermorefractive glasses and the effect of temperature onthe luminescence spectra of photo-thermorefractive glasses. 2013 Elsevier B.V. All rights reserved.

  • Influence of Halides on the Luminescence of Silver Molecular Clusters in Photo-thermo-refractive Glasses
    2013
    Co-Authors: Victor Dubrovin, A. I. Ignatiev, Nikolay Nikonorov, Alexander I. Sidorov
    Abstract:

    The luminescence spectra of silver Molecular Clusters in photo-thermo-refractive glasses are investigated in detail before and after the UV irradiation and also after the heat treatment of the samples. Also investigated are (I) the influence of halogens such as Cl and Br in glass matrix composition on the luminescence of silver Molecular Clusters in photo-thermo-refractive glasses and (II) the effect of temperature on the luminescence spectra and the integrated intensity of luminescence of photo-thermo-refractive glasses.