| 1. |
- 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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| 2. |
- 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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| 3. |
- Gisselbrecht, Mathieu, et al.
(författare)
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Size dependent fragmentation of argon clusters in the soft x-ray ionization regime.
- 2008
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 128:4
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Tidskriftsartikel (refereegranskat)abstract
- Photofragmentation of argon clusters of average size ranging from 10 up to 1000 atoms is studied using soft x-ray radiation below the 2p threshold and multicoincidence mass spectroscopy technique. For small clusters (N=10), ionization induces fast fragmentation with neutral emission imparting a large amount of energy. While the primary dissociation takes place on a picosecond time scale, the fragments undergo slow degradation in the spectrometer on a microsecond time scale. For larger clusters (N>/=100) we believe that we observe the fragmentation pattern of multiply charged species on a time-scale which lasts a few hundred nanoseconds. The reason for these slower processes is the large number of neutral atoms which act as an efficient cooling bath where the excess energy ("heat") dissipates among all degrees of freedom. Further degradation of the photoionic cluster in spectrometer then takes place on the microsecond time scale, similar to small clusters.
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| 4. |
- Lindblad, A., et al.
(författare)
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Charge delocalization dynamics of ammonia in different hydrogen bonding environments : free clusters and in liquid water solution
- 2009
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 11:11, s. 1758-1764
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Tidskriftsartikel (refereegranskat)abstract
- Valence and core level photoelectron spectra and Auger electron spectra of ammonia in pure clusters have been measured. The Auger electro spectra of gas-phase ammonia, pure ammonia clusters and ammonia in aqueous solution are compared and interpreted via ab initio calculations of the Auger spectrum of the ammonia monomer and dimer. The calculations reveal that the final two-hole valence states can be delocalized over both ammonia molecules. Features at energies pertaining to delocalized states involving one, or more, hydroge bonding orbitals can be found in both the ammonia cluster Auger electron spectrum and in that of the liquid solvated molecule. The lower Coulombic repulsion between two delocalized valence final state holes gives higher kinetic energy of the Auger electrons which is also observed in the spectra. This decay path-specific to the condensed phase-is responsible for more than 5% of the total cluster Auger intensity. Moreover, this interpretation is also applicable to the solid phase since the same features have been observed, but not assigned, in the Auger spectrum of solid ammonia.
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| 5. |
- Lindblad, A, et al.
(författare)
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The geometric structure of pure SF6 and mixed Ar/SF6 clusters investigated by core level photoelectron spectroscopy
- 2009
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 603:3, s. 433-436
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Tidskriftsartikel (refereegranskat)abstract
- The S 2p core level photoelectron spectra of Sulphurhexafluoride Clusters have been investigated together with heterogeneous Ar/SF6 clusters, created by doping Ar host clusters (with a mean size of 3600 atoms) with the molecule. Surface and bulk features are resolved both in the argon 2p and the sulphur 2p core level photoelectron spectra. For the latter level such features were only observed in the pure cluster case; a single feature characterizes the S 2p core level spectra of SF6 doped argon clusters. From the chemical shifts, investigated with respect to SF6 doping pressure. It can be concluded that the host clusters get smaller with increasing doping pressures and that the SF6 molecules predominantly stay below the cluster surface, whereas the Argon core stays intact. We have neither observed features corresponding to SF6 on the cluster Surface, nor features corresponding to molecules deep inside the bulk in any of the spectra from the pick-up experiments.
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| 6. |
- 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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| 7. |
- Lundwall, Marcus, et al.
(författare)
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Preferential site occupancy observed in coexpanded argon-krypton clusters
- 2006
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 74:4, s. 043206-
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Tidskriftsartikel (refereegranskat)abstract
- Free heterogeneous argon-krypton clusters have been produced by coexpansion and investigated by means of x-ray photoelectron spectroscopy. By examining cluster surface and bulk binding energy shifts, relative intensities, and peak widths, we show that in the mixed argon-krypton clusters the krypton atoms favor the bulk and argon atoms are pushed to the surface. Furthermore, we show that krypton atoms in the surface layer occupy high-coordination sites and that heterogeneous argon-krypton clusters produced by coexpansion show the same surface structure as argon host clusters doped with krypton. These observations are supported by site-dependent calculations of chemical shifts.
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| 8. |
- Lundwall, M., et al.
(författare)
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Preferential site occupancy of krypton atoms on free argon-cluster surfaces
- 2006
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 125:1
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Tidskriftsartikel (refereegranskat)abstract
- Argon clusters have been doped with krypton atoms in a pick-up setup and investigated by means of ultraviolet and x-ray photoelectron spectroscopy (UPS and XPS). The width of the krypton surface feature in the XPS spectra from mixed krypton/argon clusters has been studied and found to be narrower than in the case of homogeneous krypton clusters. By considering known spectral broadening mechanisms of the cluster features and the electron binding energy shift of the cluster surface feature relative to the atomic signal, we conclude that krypton ad-atoms preferentially occupy high-coordination surface sites on the argon host-cluster. (c) 2006 American Institute of Physics.
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| 9. |
- Lundwall, Marcus, et al.
(författare)
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Self-assembled heterogeneous argon/neon core-shell clusters studied by photoelectron spectroscopy
- 2007
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 126:21, s. 214706-
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Tidskriftsartikel (refereegranskat)abstract
- Clusters formed by a coexpansion process of argon and neon have been studied using synchrotron radiation. Electrons from interatomic Coulombic decay as well as ultraviolet and x-ray photoelectron spectroscopy were used to determine the heterogeneous nature of the clusters and the cluster structure. Binary clusters of argon and neon produced by coexpansion are shown to exhibit a core-shell structure placing argon in the core and neon in the outer shells. Furthermore, the authors show that 2 ML of neon on the argon core is sufficient for neon valence band formation resembling the neon solid. For 1 ML of neon the authors observe a bandwidth narrowing to about half of the bulk value.
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| 10. |
- Lundwall, M., et al.
(författare)
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Shell-dependent core-level chemical shifts observed in free xenon clusters
- 2006
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 39:24, s. 5225-5235
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Tidskriftsartikel (refereegranskat)abstract
- Photoelectron and Auger electron spectra following Xe-3d and Xe-4d ionization of free xenon clusters have been measured using synchrotron radiation. The atom-to-surface and atom-to-bulk binding energy shifts found in the Xe-3d and the subsequent M5N4,5N4,5 Auger decay are about 15% larger than those observed in the Xe-4d and N4,5O2,3O2,3 measurements. This experimental result is also considered theoretically.
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