| 1. |
- Johansson, Sofia M., 1983, et al.
(författare)
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A novel gas-vacuum interface for environmental molecular beam studies
- 2017
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 88:3
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Tidskriftsartikel (refereegranskat)abstract
- Molecular beam techniques are commonly used to obtain detailed information about reaction dynamics and kinetics of gas-surface interactions. These experiments are traditionally performed in vacuum and the dynamic state of surfaces under ambient conditions is thereby excluded from detailed studies. Herein we describe the development and demonstration of a new vacuum-gas interface that increases the accessible pressure range in environmental molecular beam (EMB) experiments. The interface consists of a grating close to a macroscopically flat surface, which allows for experiments at pressures above 1 Pa including angularly resolved measurements of the emitted flux. The technique is successfully demonstrated using key molecular beam experiments including elastic helium and inelastic water scattering from graphite, helium and light scattering from condensed adlayers, and water interactions with a liquid 1-butanol surface. The method is concluded to extend the pressure range and flexibility in EMB studies with implications for investigations of high pressure interface phenomena in diverse fields including catalysis, nanotechnology, environmental science, and life science. Potential further improvements of the technique are discussed. Published by AIP Publishing.
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| 2. |
- Johansson, Sofia M., 1983, et al.
(författare)
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Experimental and Computational Study of Molecular Water Interactions with Condensed Nopinone Surfaces Under Atmospherically Relevant Conditions
- 2020
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 124:18, s. 3652-3661
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Tidskriftsartikel (refereegranskat)abstract
- Water and organics are omnipresent in the atmosphere, and their interactions influence the properties and lifetime of both aerosols and clouds. Nopinone is one of the major reaction products formed from beta-pinene oxidation, a compound emitted by coniferous trees, and it has been found in both gas and particle phases in the atmosphere. Here, we investigate the interactions between water molecules and nopinone surfaces by combining environmental molecular beam (EMB) experiments and molecular dynamics (MD) simulations. The EMB method enables detailed studies of the dynamics and kinetics of water interacting with solid nopinone at 170-240 K and graphite coated with a molecularly thin nopinone layer at 200-270 K. MD simulations that mimic the experimental conditions have been performed to add insights into the molecular-level processes. Water molecules impinging on nopinone surfaces are efficiently trapped (>= 97%), and only a minor fraction scatters inelastically while maintaining 35-65% of their incident kinetic energy (23.2 +/- 1.0 kJ mol(-1)). A large fraction (60-80%) of the trapped molecules desorbs rapidly, whereas a small fraction (20-40%) remains on the surface for more than 10 ms. The MD calculations confirm both rapid water desorption and the occurrence of strongly bound surface states. A comparison of the experimental and computational results suggests that the formation of surface-bound water clusters enhances water uptake on the investigated surfaces.
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| 3. |
- Johansson, Sofia M., 1983
(författare)
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Molecular-Level Investigations of Water-Organic Systems of Atmospheric Relevance
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- It is known that aerosol particles may have warming and/or cooling effects on the climate and negative health effects that depend on their chemical and physical properties. However, current understanding of atmospheric particles’ effects is poor due to the diversity of their constituents and associated variations in properties. Important components are volatile organic compounds that are emitted from both natural and anthropogenic sources into the atmosphere and may condense onto existing particles or nucleate and contribute to formation of new particles. Organics may account for 20 to 90% of particles’ mass, and some may be enriched at particles’ surfaces while others are mixed in their bulk. This may substantially influence particles’ hygroscopicity, which is highly significant as particles’ water contents strongly affect their other physical and chemical properties. The water content may influence particle viscosity, which has feedbacks on gas-particle partitioning patterns and diffusion within the particles, and hence the chemical composition of both the gas and particle phases. Particles’ hygroscopicity also influences the critical supersaturation required for droplet activation, and thus affects cloud physics. The hygroscopicity also influences the radiative forcing of particles. However, there are needs for better fundamental understanding of interface processes on aerosol particle surfaces. Hence, ways to improve knowledge of these interactions are required. The Environmental Molecular Beam (EMB) technique can provide valuable information about the dynamics and kinetics of gas-surface interactions at near-ambient pressures. Thus, it may help efforts to elucidate processes at atmospherically relevant surfaces, so the doctoral project that led to this thesis focused on its uses, limitations and possible refinements. The thesis is based on five papers. The first presents and evaluates improvements to an EMB instrument, involving introduction of a grated interface between the high pressure and high vacuum regions. The improved instrument has demonstrated utility for studying water interactions with volatile surfaces, at higher than previously possible experimental pressures (up to 1 Pa). The grated interface also enables angular-resolved measurements, which are essential for complete understanding of the gas-surface processes taking place during EMB experiments. The other papers present results from four EMB studies of interactions between water and organic surfaces consisting of condensed layers of nopinone, n-butanol or valeric acid (chosen as proxies for atmospherically relevant compounds). The investigations showed that these experimental surfaces may have water trapping probabilities close to unity (≥ 94%), and accommodate water to varying extents. They also showed that desorption kinetics are significantly influenced by functional groups present on the surfaces, the degree to which these groups facilitate water binding, and the surfaces’ phase state. Accommodation coefficients were found to range from 5 to 40% on solid surfaces and up to to 90% on liquid surfaces.
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| 4. |
- Johansson, Sofia M., 1983, et al.
(författare)
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The Dynamics and Kinetics of Water Interactions with a Condensed Nopinone Surface.
- 2017
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Ingår i: The journal of physical chemistry. A. - : American Chemical Society (ACS). - 1520-5215 .- 1089-5639. ; 121:35, s. 6614-6619
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Tidskriftsartikel (refereegranskat)abstract
- Water and organic molecules are omnipresent in the environment, and their interactions are of central importance in many Earth system processes. Here we investigate molecular-level interactions between water and a nopinone surface using an environmental molecular beam (EMB) technique. Nopinone is a major reaction product formed during oxidation of β-pinene, a prominent compound emitted by coniferous trees, which has been found in both the gas and particle phases of atmospheric aerosol. The EMB method enables detailed studies of the dynamics and kinetics of D2O molecules interacting with a solid nopinone surface at 202 K. Hyperthermal collisions between water and nopinone result in efficient trapping of water molecules, with a small fraction that scatter inelastically after losing 60-80% of their incident kinetic energy. While the majority of the trapped molecules rapidly desorb with a time constant τ less than 10 μs, a substantial fraction (0.32 ± 0.09) form strong bonds with the nopinone surface and remain in the condensed phase for milliseconds or longer. The interactions between water and nopinone are compared to results for recently studied water-alcohol and water-acetic acid systems, which display similar collision dynamics but differ with respect to the kinetics of accommodated water. The results contribute to an emerging surface science-based view and molecular-level description of organic aerosols in the atmosphere.
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| 5. |
- Johansson, Sofia M., 1983, et al.
(författare)
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Understanding water interactions with organic surfaces: environmental molecular beam and molecular dynamics studies of the water-butanol system
- 2019
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 21:3, s. 1141-1151
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Tidskriftsartikel (refereegranskat)abstract
- The interactions between water molecules and condensed n-butanol surfaces are investigated at temperatures from 160 to 240 K using the environmental molecular beam experimental method and complementary molecular dynamics (MD) simulations. In the experiments hyperthermal water molecules are directed onto a condensed n-butanol layer and the flux from the surface is detected in different directions. A small fraction of the water molecules scatters inelastically from the surface while losing 60-90% of their initial kinetic energy in collisions, and the angular distributions of these molecules are broad for both solid and liquid surfaces. The majority of the impinging water molecules are thermalized and trapped on the surface, while subsequent desorption is governed by two different processes: one where molecules bind briefly to the surface (residence time < 10 s), and another where the molecules trap for a longer time = 0.8-2.0 ms before desorbing. Water molecules trapped on a liquid n-butanol surface are substantially less likely to escape from the surface compared to a solid layer. The MD calculations provide detialed insight into surface melting, adsorption, absorption and desorption processes. Calculated angular distributions and kinetic energy of emitted water molecules agree well with the experimental data. In spite of its hydrophobic tail and enhanced surface organization below the melting temperature, butanol's hydrophilic functional groups are concluded to be surprisingly accessible to adsorbed water molecules; a finding that may be explained by rapid diffusion of water away from hydrophobic surface structures towards more strongly bound conformational structures.
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| 6. |
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| 7. |
- Kong, Xiangrui, et al.
(författare)
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Water Accommodation on Ice and Organic Surfaces: Insights from Environmental Molecular Beam Experiments
- 2014
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 118:47, s. 13378-13386
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Tidskriftsartikel (refereegranskat)abstract
- Water uptake on aerosol and cloud particles in the atmosphere modifies their chemistry and microphysics with important implications for climate on Earth. Here, we apply an environmental molecular beam (EMB) method to characterize water accommodation on ice and organic surfaces. The adsorption of surface-active compounds including short-chain alcohols, nitric acid, and acetic acid significantly affects accommodation of D2O on ice. n-Hexanol and n-butanol adlayers reduce water uptake by facilitating rapid desorption and function as inefficient barriers for accommodation as well as desorption of water, while the effect of adsorbed methanol is small. Water accommodation is close to unity on nitric-acid- and acetic-acid-covered ice, and accommodation is significantly more efficient than that on the bare ice surface. Water uptake is inefficient on solid alcohols and acetic acid but strongly enhanced on liquid phases including a quasi-liquid layer on solid n-butanol. The EMB method provides unique information on accommodation and rapid kinetics on volatile surfaces, and these studies suggest that adsorbed organic and acidic compounds need to be taken into account when describing water at environmental interfaces.
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