| 1. |
- Kaiser, L., et al.
(författare)
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Angular emission distribution of O 1s photoelectrons of uniaxially oriented methanol
- 2020
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 53:19
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Tidskriftsartikel (refereegranskat)abstract
- The angular distribution of O 1s photoelectrons emitted from uniaxially oriented methanol is studied experimentally and theoretically. We employed circularly polarized photons of an energy ofh nu= 550 eV for our investigations. We measured the three-dimensional photoelectron angular distributions of methanol, with the CH3-OH axis oriented in the polarization plane, by means of cold target recoil ion momentum spectroscopy. The experimental results are interpreted by single active electron calculations performed with the single center method. A comparative theoretical study of the respective molecular-frame angular distributions of O 1s photoelectrons of CO, performed for the same photoelectron kinetic energy and for a set of different internuclear distances, allows for disentangling the role of internuclear distance and the hydrogen atoms of methanol as compared to carbon monoxide.
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| 2. |
- Saak, Clara-Magdalena, et al.
(författare)
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Proton dynamics in molecular solvent clusters as an indicator for hydrogen bond network strength in confined geometries
- 2020
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : ROYAL SOC CHEMISTRY. - 1463-9076 .- 1463-9084. ; 22:6, s. 3264-3272
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen bonding leads to the formation of strong, extended intermolecular networks in molecular liquids such as water. However, it is less well-known how robust the network is to environments in which surface formation or confinement effects become prominent, such as in clusters or droplets. Such systems provide a useful way to probe the robustness of the network, since the degree of confinement can be tuned by altering the cluster size, changing both the surface-to-volume ratio and the radius of curvature. To explore the formation of hydrogen bond networks in confined geometries, here we present O 1s Auger spectra of small and large clusters of water, methanol, and dimethyl ether, as well as their deuterated equivalents. The Auger spectra of the clusters and the corresponding macroscopic liquids are compared and evaluated for an isotope effect, which is due to proton dynamics within the lifetime of the core hole (proton-transfer-mediated charge-separation, PTM-CS), and can be linked to the formation of a hydrogen bond network in the system. An isotope effect is observed in water and methanol but not for dimethyl ether, which cannot donate a hydrogen bond at its oxygen site. The isotope effect, and therefore the strength of the hydrogen bond network, is more pronounced in water than in methanol. Its value depends on the average size of the cluster, indicating that confinement effects change proton dynamics in the core ionised excited state.
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| 3. |
- Saak, Clara-Magdalena, et al.
(författare)
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Temperature Dependence of X-ray-Induced Auger Processes in Liquid Water
- 2020
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Ingår i: The Journal of Physical Chemistry Letters. - : AMER CHEMICAL SOC. - 1948-7185. ; 11:7, s. 2497-2501
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Tidskriftsartikel (refereegranskat)abstract
- Auger spectroscopy has previously been used to study changes in the hydrogen bond network in liquid water, but to the best of our knowledge it has not been used to track such changes as a function of temperature. We show Auger spectroscopy to reflect the weakening of the hydrogen bond network upon heating. This shows that the radiation response of water, i.e., the relative propensity of the different processes occurring after radiation exposure, including femtosecond proton dynamics, depends on the temperature of the system. This proof-of-principle study further demonstrates the suitability of the technique to help elucidate information on the intermolecular structure of liquids such as water, opening the door to further temperature-dependent studies.
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| 4. |
- Unger, Isaak, et al.
(författare)
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Influence of Organic Acids on the Surface Composition of Sea Spray Aerosol
- 2020
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 124:2, s. 422-429
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies on sea spray aerosol indicate an enrichment of Ca2+ in small particles, which are often thought to originate from the very surface of a water body when bubbles burst. One model to explain this observation is the formation of ion pairs between Ca2+(aq) and surface-active organic species. In this study, we have used X-ray photoelectron spectroscopy to probe aqueous salt solutions and artificial sea spray aerosol to study whether ion pairing in the liquid environment also affects the surface composition of dry aerosol. Carboxylic acids were added to the sample solutions to mimic some of the organic compounds present in natural seawater. Our results show that the formation of a core-shell structure governs the surface composition of the aerosol. The core-shell structure contrasts previous observations of the dry sea spray aerosol on substrates. As such, this may indicate that substrates can impact the morphology of the dried aerosol.
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