| 1. |
- Gopakumar, Geethanjali, et al.
(författare)
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Probing aqueous ions with non-local Auger relaxation
- 2022
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 24:15, s. 8661-8671
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Tidskriftsartikel (refereegranskat)abstract
- Non-local analogues of Auger decay are increasingly recognized as important relaxation processes in the condensed phase. Here, we explore non-local autoionization, specifically Intermolecular Coulombic Decay (ICD), of a series of aqueous-phase isoelectronic cations following 1s core-level ionization. In particular, we focus on Na+, Mg2+, and Al3+ ions. We unambiguously identify the ICD contribution to the K-edge Auger spectrum. The different strength of the ion-water interactions is manifested by varying intensities of the respective signals: the ICD signal intensity is greatest for the Al3+ case, weaker for Mg2+, and absent for weakly-solvent-bound Na+. With the assistance of ab initio calculations and molecular dynamics simulations, we provide a microscopic understanding of the non-local decay processes. We assign the ICD signals to decay processes ending in two-hole states, delocalized between the central ion and neighbouring water. Importantly, these processes are shown to be highly selective with respect to the promoted water solvent ionization channels. Furthermore, using a core-hole-clock analysis, the associated ICD timescales are estimated to be around 76 fs for Mg2+ and 34 fs for Al3+. Building on these results, we argue that Auger and ICD spectroscopy represents a unique tool for the exploration of intra- and inter-molecular structure in the liquid phase, simultaneously providing both structural and electronic information.
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| 2. |
- Hans, Andreas, et al.
(författare)
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Optical Fluorescence Detected from X-ray Irradiated Liquid Water
- 2017
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 121:10, s. 2326-2330
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Tidskriftsartikel (refereegranskat)abstract
- Despite its importance, the structure and dynamics of liquid water are still poorly understood in many apsects. Here, we report on the observation of optical fluorescence upon soft X-ray irradiation of liquid water. Detection of spectrally resolved fluorescence was achieved by a combination of the liquid microjet technique and fluorescence spectroscopy. We observe a genuine liquid-phase fluorescence manifested by a broad emission band in the 170-340 nm (4-7 eV) photon wavelength range. In addition, another narrower emission near 300 nm can be assigned to the fluorescence of OH (A state) in the gas phase, the emitting species being formed by Auger electrons escaping from liquid water. We argue that the newly observed broad-band emission of liquid water is relevant in search of extraterrestrial life, and we also envision the observed electron-ejection mechanism to find application for exploring solutes at liquid vapor interfaces.
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| 3. |
- Hans, Andreas, et al.
(författare)
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Soft X-ray induced ultraviolet fluorescence emission from bulk and interface of a liquid water microjet
- 2017
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Ingår i: Journal of Physics, Conference Series. - : Institute of Physics Publishing (IOPP). - 1742-6588 .- 1742-6596. ; 875
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Tidskriftsartikel (refereegranskat)abstract
- Tremendous progress has been made in the research on the structure and dynamics of liquids due to the development of advanced experimental techniques such as liquid microjets, enabling investigations on volatile samples in ultrahigh vacuum environments. The spectroscopy of charged particles, e.g. photoelectron or Auger electron spectroscopy on liquids, is an established field by now. Here, we report on the successful application of a fluorescence spectrometer to measure optical emission spectra from liquids irradiated with soft X-ray synchrotron radiation.
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| 4. |
- Heyda, Jan, et al.
(författare)
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Reversal of Hofmeister Ordering for Pairing of NH4+ vs Alkylated Ammonium Cations with Halide Anions in Water
- 2010
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 114:33, s. 10843-10852
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Tidskriftsartikel (refereegranskat)abstract
- Pairing of halide anions with ammonium, as well as with trialkylated and tetraalkylated ammonium cations in water, is investigated by molecular dynamics simulations, which are verified by ab initio calculations and experimental excess chemical potentials. We find that ammonium prefers to pair with smaller halides over the larger ones, while the order is reversed for tetraalkylated ammonium cations. Trialkylated ammonium cations exhibit an intermediate behavior, with the acidic hydrogen preferring smaller anions and alkyl chains interacting attractively with larger halides. This Hofmeister reversal of anionic ordering upon tetraalkylation of the ammonium cation is robustly predicted by both nonpolarizable and polarizable force fields and supported by experimental evidence.
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| 5. |
- Richter, Clemens, et al.
(författare)
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Competition between proton transfer and intermolecular Coulombic decay in water
- 2018
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Ingår i: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Intermolecular Coulombic decay (ICD) is a ubiquitous relaxation channel of electronically excited states in weakly bound systems, ranging from dimers to liquids. As it is driven by electron correlation, it was assumed that it will dominate over more established energy loss mechanisms, for example fluorescence. Here, we use electron-electron coincidence spectroscopy to determine the efficiency of the ICD process after 2a(1) ionization in water clusters. We show that this efficiency is surprisingly low for small water clusters and that it gradually increases to 40-50% for clusters with hundreds of water units. Ab initio molecular dynamics simulations reveal that proton transfer between neighboring water molecules proceeds on the same timescale as ICD and leads to a configuration in which the ICD channel is closed. This conclusion is further supported by experimental results from deuterated water. Combining experiment and theory, we infer an intrinsic ICD lifetime of 12-52 fs for small water clusters.
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| 6. |
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| 7. |
- Tóth, Peter, et al.
(författare)
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Radiocarbin dating of grass-tempered ceramic reveals the earliest pottery from Slovakia predates the arrival of farming
- 2023
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Ingår i: Radiocarbon. - 0033-8222 .- 1945-5755. ; 65:3, s. 733-753
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Tidskriftsartikel (refereegranskat)abstract
- In the absence of wood, bone, and other organics, one possible candidate for determining the age of a site is the radiocarbon (14C) dating of pottery. In central Europe during the Early Neolithic, pottery was ubiquitous and contained substantial quantities of organic temper. However, attempts at the direct dating of organic inclusions raises a lot of methodological issues, especially when several sources of carbon contribute to the resulting radiocarbon age. Hence an alternative approach to dating of the early pottery is necessary. Here, we present a novel method of bulk separation of organic content from the grass-tempered pottery from Santovka (Slovakia). The procedure is based on the consecutive application of three inorganic acids, dissolving clay, silica content, and low molecular or mobile fractions to separate organic inclusions added to the pottery matrix during the formation of vessels. Radiocarbon dates obtained with this method are coherent and produce the shortest time span compared to other pretreatment methods presented in this study. The paired dates of grass-tempered pots with the 14C age of lipids extracted from the same pots point to a difference of 400–600 14C yr, however they are in line with the site’s chronostratigraphic Bayesian model. Grass-tempered pottery from Santovka (Slovakia) is dated to the first half of the 6th millennium cal BC, making it the earliest pottery north of the Danube. It seems feasible that ceramic containers from Santovka were produced by hunter-gatherers, and pottery predated the arrival of farming in the Carpathian region by a couple of centuries.
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| 8. |
- Unger, Isaak, et al.
(författare)
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Observation of electron-transfer-mediated decay in aqueous solution
- 2017
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Ingår i: Nature Chemistry. - : NATURE PUBLISHING GROUP. - 1755-4330 .- 1755-4349. ; 9:7, s. 708-714
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Tidskriftsartikel (refereegranskat)abstract
- Photoionization is at the heart of X-ray photoelectron spectroscopy (XPS), which gives access to important information on a sample's local chemical environment. Local and non-local electronic decay after photoionization-in which the refilling of core holes results in electron emission from either the initially ionized species or a neighbour, respectively-have been well studied. However, electron-transfer-mediated decay (ETMD), which involves the refilling of a core hole by an electron from a neighbouring species, has not yet been observed in condensed phase. Here we report the experimental observation of ETMD in an aqueous LiCl solution by detecting characteristic secondary low-energy electrons using liquid-microjet soft XPS. Experimental results are interpreted using molecular dynamics and high-level ab initio calculations. We show that both solvent molecules and counterions participate in the ETMD processes, and different ion associations have distinctive spectral fingerprints. Furthermore, ETMD spectra are sensitive to coordination numbers, ion-solvent distances and solvent arrangement.
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