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| 2. |
- Bergersen, Henrik, et al.
(författare)
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First observation of vibrations in core-level photoelectron spectra of free neutral molecular clusters
- 2006
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 429:1-3, s. 109-113
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Tidskriftsartikel (refereegranskat)abstract
- Core-level photoelectron spectra of free neutral methane clusters have been recorded. These spectra exhibit well-resolved surface and bulk features as well as vibrational fine structure. The vibrational structure in the cluster signal is well reproduced by a theoretical model that assumes independent contributions from inter- and intramolecular modes. The intramolecular contribution to the vibrational line-shape is taken to be equal to that of the monomer in the gas phase, while the intermolecular part is simplified to line broadening. An estimate of the cluster size has been made on the basis of the observed surface-to-bulk intensity ratio.
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| 3. |
- Bergersen, Henrik, et al.
(författare)
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Two size regimes of methanol clusters produced by adiabatic expansion
- 2006
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 125:18, s. 184303-
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Tidskriftsartikel (refereegranskat)abstract
- Free neutral methanol clusters produced by adiabatic expansion have been studied by photoelectron spectroscopy and line shape modeling. The results show that clusters belonging to two distinct size regimes can be produced by changing the expansion conditions. While the larger size regime can be well described by line shapes calculated for clusters consisting of hundreds of molecules, the smaller size regime corresponds to methanol oligomers, predominantly of cyclic structure. There is little contribution from dimers to the spectra.
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| 4. |
- Gopakumar, Geethanjali, 1992-, et al.
(författare)
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X-ray Induced Fragmentation of Protonated Cystine
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Protein structure determination using high-intensity X-ray sources induces damage in the protein. Disulfide bridges, formed between two cysteine amino acid residues stabilize the protein structure. Owing to the higher absorption cross-section of sulfur for X-ray photons, and a large number of electrons released from sulfur atoms, these disulfide bridges are hot spots for a higher level of noise in structural studies. But it is yet to be understood how exactly the damage occurs through the interaction of the disulfide bridges with photons. Here we study the fragmentation of protonated cystine in the gas phase, which is the dimer of cysteine, by irradiation with X-rays across the sulfur L-edge using an electrospray ionization source (ESI) in combination with an ion trap. This is complemented with the calculation of the sulfur NEXAFS spectrum on the level of Restricted Open-Shell Configuration Interaction (ROCIS) and Density Functional Theory (DFT) calculations for molecular orbital visualization as well as Molecular Dynamics (MD) simulations for the fragmentation of triply charged cystine ions. We have deduced a possible pathway of fragmentation upon excitation and ionization of S 2p electrons by combining the experiments and simulations. The disulfide bridge breaks for resonant excitation at lower energies but remains intact upon higher energy resonant excitation and upon ionization of S 2p. The larger fragments formed subsequently break into smaller fragments.
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| 5. |
- 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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| 6. |
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| 7. |
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| 8. |
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| 9. |
- Lundwall, M., et al.
(författare)
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Neighbor-induced photoelectron recapture in argon clusters : A photon-energy-dependent study of Auger spectra
- 2008
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 78:6, s. 065201-
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Tidskriftsartikel (refereegranskat)abstract
- A photon-energy-dependent experimental study of the L2,3M2,3M2,3 Auger transitions in argon clusters is presented, and features without atomic counterparts are observed in the spectra up to photon energies at least 30 eV above the L2,3 threshold. We propose that these features are due to the process of neighbor-induced recapture, in which the outgoing photoelectron is backscattered by neighboring atoms in the cluster, loses energy in a Bremsstrahlung-like inverse photoemission process, and is recaptured in a Rydberg orbital of the core-ionized atom before Auger decay.
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| 10. |
- Lundwall, Marcus, et al.
(författare)
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Photon energy dependent intensity variations observed in Auger spectra of free argon clusters
- 2006
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 39:16, s. 3321-3333
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Tidskriftsartikel (refereegranskat)abstract
- Photon energy dependent intensity variations are experimentally observed in the L2,3M2,3M2,3 Auger spectra of argon clusters. Two cluster sizes are examined in the present study. Extrinsic scattering effects, both elastic and inelastic, involving the photoelectron are discussed and suggested as the explanation of the variations in the Auger signal. The atoms in the first few coordination shells surrounding the core-ionized atom are proposed to be the main targets for the scattering processes.
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