| 1. |
- Ablyasova, Olesya S., et al.
(författare)
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Electronic Structure of the Complete Series of Gas-Phase Manganese Acetylacetonates by X-ray Absorption Spectroscopy
- 2023
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 127:34, s. 7121-7131
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Tidskriftsartikel (refereegranskat)abstract
- Metal centers in transition metal–ligand complexes occur in a variety of oxidation states causing their redox activity and therefore making them relevant for applications in physics and chemistry. The electronic state of these complexes can be studied by X-ray absorption spectroscopy, which is, however, due to the complex spectral signature not always straightforward. Here, we study the electronic structure of gas-phase cationic manganese acetylacetonate complexes Mn(acac)1–3+ using X-ray absorption spectroscopy at the metal center and ligand constituents. The spectra are well reproduced by multiconfigurational wave function theory, time-dependent density functional theory as well as parameterized crystal field and charge transfer multiplet simulations. This enables us to get detailed insights into the electronic structure of ground-state Mn(acac)1–3+ and extract empirical parameters such as crystal field strength and exchange coupling from X-ray excitation at both the metal and ligand sites. By comparison to X-ray absorption spectra of neutral, solvated Mn(acac)2,3 complexes, we also show that the effect of coordination on the L3 excitation energy, routinely used to identify oxidation states, can contribute about 40–50% to the observed shift, which for the current study is 1.9 eV per oxidation state.
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| 2. |
- Bari, Sadia, et al.
(författare)
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Soft X-ray Spectroscopy as a Probe for Gas-Phase Protein Structure : Electron Impact Ionization from Within
- 2018
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539. ; 24:30, s. 7631-7636
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Tidskriftsartikel (refereegranskat)abstract
- Preservation of protein conformation upon transfer into the gas phase is key for structure determination of free single molecules, for example using X-ray free-electron lasers. In the gas phase, the helicity of melittin decreases strongly as the protein's protonation state increases. We demonstrate the sensitivity of soft X-ray spectroscopy to the gas-phase structure of melittin cations ([melittin+qH]q+, q=2-4) in a cryogenic linear radiofrequency ion trap. With increasing helicity, we observe a decrease of the dominating carbon 1s-π* transition in the amide C=O bonds for non-dissociative single ionization and an increase for non-dissociative double ionization. As the underlying mechanism we identify inelastic electron scattering. Using an independent atom model, we show that the more compact nature of the helical protein conformation substantially increases the probability for off-site intramolecular ionization by inelastic Auger electron scattering.
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| 3. |
- Couto, Rafael Carvalho, et al.
(författare)
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The carbon and oxygen K-edge NEXAFS spectra of CO
- 2020
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 22:28, s. 16215-16223
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Tidskriftsartikel (refereegranskat)abstract
- We present and analyze high resolution near edge X-ray absorption fine structure (NEXAFS) spectra of CO+ at the carbon and oxygen K-edges. The spectra show a wealth of features that appear very differently at the two K-edges. The analysis of these features can be divided into three parts; (i) repopulation transition to the open shell orbital – here the C(1s) or O(1s) to 5σ transition, where the normal core hole state is reached from a different initial state and different interaction than in X-ray photoelectron spectroscopy; (ii) spin coupled split valence bands corresponding to C(1s) or O(1s) to π* transitions; (iii) remainder weak and long progressions towards the double ionization potentials containing a manifold of peaks. These parts, none of which has correspondence in NEXAFS spectra of neutral molecules, are dictated by the localization of the singly occupied 5σ orbital, adding a dimension of chemistry to the ionic NEXAFS technique.
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| 4. |
- Delcey, Mickael G, 1988-, et al.
(författare)
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Soft X-ray signatures of cationic manganese–oxo systems, including a high-spin manganese(v) complex
- 2022
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 24:6, s. 3598-3610
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Tidskriftsartikel (refereegranskat)abstract
- Limitations in synthesis of high-valent metal–oxo complexes are circumvented by trapping a series of ionic Mn–oxo complexes. One of them is a rare high-spin Mn(v)–oxo, which can serve as a template to identify similar intermediates in catalysis.
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| 5. |
- Egorov, Dmitrii, et al.
(författare)
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Near-Edge Soft X-ray Absorption Mass Spectrometry of Protonated Melittin
- 2018
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Ingår i: Journal of the American Society for Mass Spectrometry. - : American Chemical Society (ACS). - 1044-0305. ; 29:11, s. 2138-2151
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the photoionization and photofragmentation yields of gas-phase multiply protonated melittin cations for photon energies at the K-shell absorption edges of carbon, nitrogen, and oxygen. Two similar experimental approaches were employed. In both experiments, mass selected [melittin+qH]q+ (q=2–4) ions were accumulated in radiofrequency ion traps. The trap content was exposed to intense beams of monochromatic soft X-ray photons from synchrotron beamlines and photoproducts were analyzed by means of time-of-flight mass spectrometry. Mass spectra were recorded for fixed photon energies, and partial ion yield spectra were recorded as a function of photon energy. The combination of mass spectrometry and soft X-ray spectroscopy allows for a direct correlation of protein electronic structure with various photoionization channels. Non-dissociative single and double ionization are used as a reference. The contribution of both channels to various backbone scission channels is quantified and related to activation energies and protonation sites. Soft X-ray absorption mass spectrometry combines fast energy deposition with single and double ionization and could complement established activation techniques. [Figure not available: see fulltext.].
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| 6. |
- Gopakumar, Geethanjali, 1992-, et al.
(författare)
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X-ray Induced Fragmentation of Protonated Cystine
- 2022
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 126:9, s. 1496-1503
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate site-specific X-ray induced fragmentation across the sulfur L-edge of protonated cystine, the dimer of the amino acid cysteine. Ion yield NEXAFS were performed in the gas phase using electrospray ionization (ESI) in combination with an ion trap. The interpretation of the sulfur L-edge NEXAFS spectrum is supported by Restricted Open-Shell Configuration Interaction (ROCIS) calculations. The fragmentation pathway of triply charged cystine ions was modeled by Molecular Dynamics (MD) simulations. We have deduced a possible pathway of fragmentation upon excitation and ionization of S 2p electrons. The disulfide bridge breaks for resonant excitation at lower photon energies but remains intact upon higher energy resonant excitation and upon ionization of S 2p. The larger fragments initially formed subsequently break into smaller fragments.
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| 7. |
- Haitjema, Jarich, et al.
(författare)
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Soft X-ray absorption and fragmentation of tin-oxo cage photoresists
- 2024
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Ingår i: Physical Chemistry Chemical Physics. - 1463-9076. ; 26:7, s. 5986-5998
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Tidskriftsartikel (refereegranskat)abstract
- “Tin-oxo cage” organometallic compounds are considered as photoresists for extreme ultraviolet (EUV) photolithography. To gain insight into their electronic structure and reactivity to ionizing radiation, we trapped bare gas-phase n-butyltin-oxo cage dications [(BuSn)12O14(OH)6]2+ in an ion trap and investigated their fragmentation upon soft X-ray photoabsorption by means of mass spectrometry. In complementary experiments, the tin-oxo cages with hydroxide and trifluoroacetate counter-anions were cast in thin films and studied using X-ray transmission spectroscopy. Quantum-chemical calculations were used to interpret the observed spectra. At the carbon K-edge, a distinct pre-edge absorption band can be attributed to transitions in which electrons are promoted from C1s orbitals to the lowest unoccupied molecular orbitals, which are delocalized orbitals with strong antibonding (Sn-C ?*) character. At higher energies, the most prominent resonant transitions involve C-C and C-H ?* valence states and Rydberg (3s and 3p) states. In the solid state, the onset of continuum ionization is shifted by ?5 eV to lower energy with respect to the gas phase, due to the electrostatic effect of the counterions. The O K-edge also shows a pre-edge absorption, but it is devoid of any specific features, because there are many transitions from the different O1s orbitals to a large number of vacant orbitals. In the gas phase, formation of the parent [(BuSn)12O14(OH)6]3+ radical ion is not observed at the C K-edge nor at the O K-edge, because the loss of a butyl group from this species is very efficient. We do observe a number of triply charged photofragment ions, some of which have lost up to 5 butyl groups. Structures of these species are proposed based on quantum-chemical calculations, and pathways of formation are discussed. Our results provide insight into the electronic structure of alkyltin-oxo cages, which is a prerequisite for understanding their response to EUV photons and their performance as EUV photoresists.
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| 8. |
- Leroux, Juliette, et al.
(författare)
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Mapping the electronic transitions of protonation sites in peptides using soft X-ray action spectroscopy
- 2023
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 25:37, s. 25603-25618
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Tidskriftsartikel (refereegranskat)abstract
- Near-edge X-ray absorption mass spectrometry (NEXAMS) around the nitrogen and oxygen K-edges was employed on gas-phase peptides to probe the electronic transitions related to their protonation sites, namely at basic side chains, the N-terminus and the amide oxygen. The experimental results are supported by replica exchange molecular dynamics and density-functional theory and restricted open-shell configuration with single calculations to attribute the transitions responsible for the experimentally observed resonances. We studied five tailor-made glycine-based pentapeptides, where we identified the signature of the protonation site of N-terminal proline, histidine, lysine and arginine, at 406 eV, corresponding to N 1s & RARR; & sigma;*(NHx+) (x = 2 or 3) transitions, depending on the peptides. We compared the spectra of pentaglycine and triglycine to evaluate the sensitivity of NEXAMS to protomers. Separate resonances have been identified to distinguish two protomers in triglycine, the protonation site at the N-terminus at 406 eV and the protonation site at the amide oxygen characterized by a transition at 403.1 eV.
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| 9. |
- Lindblad, Rebecka, Dr, 1984-, et al.
(författare)
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Experimental and theoretical near-edge x-ray-absorption fine-structure studies of NO
- 2022
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society. - 2469-9926 .- 2469-9934. ; 106:4
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Tidskriftsartikel (refereegranskat)abstract
- Experimental near-edge x-ray-absorption fine-structure (NEXAFS) spectra of the nitrosonium NO+ ion are presented and theoretically analyzed. While neutral NO has an open shell, the cation is a closed-shell species, which for NEXAFS leads to the simplicity of a closed-shell spectrum. Compared to neutral NO, the electrons in the cation experience a stronger Coulomb potential, which introduces a shift of the ionization potential towards higher energies, a depletion of intensity in a large interval above the pi* resonance, and a shift of the sigma* resonance from the continuum to below the ionization threshold. NEXAFS features at the nitrogen and oxygen K edges of NO+ are compared, as well as NEXAFS features at the nitrogen edges of the isoelectronic closed-shell species NO+, N2, and N2H+.
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| 10. |
- Lindblad, Rebecka, et al.
(författare)
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Experimental and theoretical near-edge x-ray-absorption fine-structure studies of NO
- 2022
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society (APS). - 2469-9926 .- 2469-9934. ; 106:4
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Tidskriftsartikel (refereegranskat)abstract
- Experimental near-edge x-ray-absorption fine-structure (NEXAFS) spectra of the nitrosonium NO+ ion are presented and theoretically analyzed. While neutral NO has an open shell, the cation is a closed-shell species, which for NEXAFS leads to the simplicity of a closed-shell spectrum. Compared to neutral NO, the electrons in the cation experience a stronger Coulomb potential, which introduces a shift of the ionization potential towards higher energies, a depletion of intensity in a large interval above the pi* resonance, and a shift of the sigma* resonance from the continuum to below the ionization threshold. NEXAFS features at the nitrogen and oxygen K edges of NO+ are compared, as well as NEXAFS features at the nitrogen edges of the isoelectronic closed-shell species NO+, N2, and N2H+.
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