| 1. |
|
|
| 2. |
|
|
| 3. |
- Bergersen, Henrik, et al.
(författare)
-
A photoelectron spectroscopic study of aqueous tetrabutylammonium iodide
- 2007
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 19:32, s. 326101-
-
Tidskriftsartikel (refereegranskat)abstract
- Photoelectron spectra of tetrabutylammonium iodide (TBAI) dissolved in water have been recorded using a novel experimental set-up, which enables photoelectron spectroscopy of volatile liquids. The set-up is described in detail. Ionization energies are reported for I− 5p, I− 4d, C 1s and N 1s. The C 1s spectrum shows evidence of inelastic scattering of the photoelectrons, that differs from the case of TBAI in formamide.
|
|
| 4. |
- Bergersen, Henrik, et al.
(författare)
-
First observation of vibrations in core-level photoelectron spectra of free neutral molecular clusters
- 2006
-
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 429:1-3, s. 109-113
-
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.
|
|
| 5. |
- Bergersen, Henrik, 1978-
(författare)
-
Free Neutral Clusters and Liquids Studied by Electron Spectroscopy and Lineshape Modeling
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The electronic and geometrical structure of free neutral clusters and liquids have been studied using synchrotron-radiation based photoelectron and Auger electron spectroscopy in combination with lineshape modeling. A novel experimental setup has been developed for studies of liquids, based on the liquid microjet technique. Theoretical lineshapes have been computed using both classical (molecular dynamics) and quantum mechanical (mainly density functional theory) methods.Clusters are finite ensembles of atoms or molecules, ranging in size from a few to several thousand atoms. Apart from being fundamentally interesting, clusters are also promising as building blocks for nano-technology. In this thesis results are presented for rare-gas and molecular clusters, ranging from weakly van-deer-Waals bonded to hydrogen bonded. It is shown that the combination of core-level photoelectron spectroscopy (XPS) and lineshape modeling can be used to estimate the sizes of clusters. A model for treating the effect of inter-molecular nuclear relaxation upon ionization is proposed. The structure of single-component molecular clusters are investigated by molecular dynamics simulations, validated against XPS data. Finally, the radial structure of a two-component molecular cluster is investigated by XPS.Liquids have been studied for centuries, but still many questions remain regarding the microscopic properties. With the recent development of the liquid microjet technique, new insight into the atomic structure can be obtained. In this thesis we study aqueous solutions using photoelectron and Auger electron spectroscopy (AES). We investigate the structure of surface active molecules by XPS, study the Auger decay after core-level ionization in aqueous potassium chloride (KCl), and follow the changes in molecular structure of glycine as a function of pH.
|
|
| 6. |
|
|
| 7. |
- Bergersen, Henrik, et al.
(författare)
-
Two size regimes of methanol clusters produced by adiabatic expansion
- 2006
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 125:18, s. 184303-
-
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.
|
|
| 8. |
- Björneholm, Olle, et al.
(författare)
-
Free clusters studied by core-level spectroscopies
- 2009
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576 .- 0167-5087. ; 601:1-2, s. 161-181
-
Forskningsöversikt (refereegranskat)abstract
- In this review we describe the development and current status of free clusters studied using core-level spectroscopies. This topic ranges from simple model systems, such as rare gas clusters, to molecular clusters, and clusters of solids, held together by ionic, covalent and metallic bonding.
|
|
| 9. |
|
|
| 10. |
|
|
| 11. |
- Fink, Reinhold, et al.
(författare)
-
Specific production of very long-lived core-excited sulfur atoms by 2p(-1)sigma* excitation of the OCS molecule followed by ultrafast dissociation
- 2006
-
Ingår i: Journal of Physics B. - 0953-4075 .- 1361-6455. ; 39:12, s. L269-L275
-
Tidskriftsartikel (refereegranskat)abstract
- A core-excited sulfur state with a lifetime almost one order of magnitude longer than in molecular 2p core-hole states is selectively produced by ultrafast dissociation of S 2p -> sigma* excited OCS. Clear evidence for this is provided by strong atomic peaks (20% of the total intensity) in x-ray fluorescence but very weak ones (2%) in the corresponding resonant Auger spectrum. Corroborating the assignment of the spectra, ab initio calculations explain the enhanced lifetime: the Auger decay of the produced D-3(3) (2p(5)3p(5)) sulfur state is strongly decreased as it contradicts a newly derived propensity rule of the L2,3MM Auger decay.
|
|
| 12. |
|
|
| 13. |
- Gisselbrecht, Mathieu, et al.
(författare)
-
Size dependent fragmentation of argon clusters in the soft x-ray ionization regime.
- 2008
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 128:4
-
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.
|
|
| 14. |
- Hergenhahn, Uwe, et al.
(författare)
-
3p valence photoelectron spectrum of Ar clusters
- 2009
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 79:15, s. 155448-
-
Tidskriftsartikel (refereegranskat)abstract
- The shape of the outer valence (3p) photoelectron spectrum of Ar clusters is investigated by vacuum ultraviolet photoionization with synchrotron radiation. We show the dependence of the spectrum on cluster size and the change in its shape with photon energy. Inelastic losses due to intracluster photoelectron scattering are most important for changes in the photoelectron main line and explain the appearance of additional peaks. A comparison of our results to earlier work on bulk condensed Ar and Ar thin films is given. Evidence for a deviation of the photoionization cross sections for clusters from the atomic ones has not been found.
|
|
| 15. |
|
|
| 16. |
|
|
| 17. |
|
|
| 18. |
- Le Guen, K., et al.
(författare)
-
H2S ultrafast dissociation probed by energy-selected resonant Auger electron–ion coincidence measurements
- 2007
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 127:11, s. 114315-
-
Tidskriftsartikel (refereegranskat)abstract
- We have studied the ultrafast dissociation of the H2S molecule upon S 2p(3/2)-> 6a(1) inner-shell excitation by combining high-resolution resonant Auger spectroscopy and energy-selected Auger electron-ion coincidence measurements. Auger final states have been correlated to the different fragmentation pathways (S+, HS+, and H2S+ ions). As an original result, we evidence a three-step mechanism to describe the resonant production of S+: the Auger recombination in the HS* fragment is followed for the A (3)Pi and c (1)Pi states by the S++H fragmentation mechanism.
|
|
| 19. |
- Lindblad, Andreas, 1978-
(författare)
-
A Treatise on the Geometric and Electronic Structure of Clusters : Investigated by Synchrotron Radiation Based Electron Spectroscopies
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Clusters are finite ensembles of atoms or molecules with sizes in the nanometer regime (i.e. nanoparticles). This thesis present results on the geometric and electronic structure of homogeneous and heterogeneous combinations of atoms and molecules. The systems have been studied with synchrotron radiation and valence, core and Auger electron spectroscopic techniques.The first theme of the thesis is that of mixed clusters. It is shown that by varying the cluster production technique both structures that are close to that predicted by equilibrium considerations can be attained as well as far from equilibrium structures.Electronic processes following ionization constitute the second theme. The post-collision interaction phenomenon, energy exchange between the photo- and the Auger electrons, is shown to be different in clusters of argon, krypton and xenon. A model is proposed that takes polarization screening in the final state into account. This result is of general character and should be applicable to the analysis of core level photoelectron and Auger electron spectra of insulating and semi-conducting bulk materials as well.Interatomic Coloumbic Decay is a process that can occur in the condensed phases of weakly bonded systems. Results on the time-scale of the process in Ne clusters and mixed Ar/Ne clusters are herein discussed, as well observations of resonant contributions to the process. In analogy to Auger vis-à-vis Resonant Auger it is found that to the ICD process there is a corresponding Resonant ICD process possible. This has later been observed in other systems and by theoretical calculations as well in subsequent works by other groups.Delocalization of dicationic valence final states in the hydrogen bonded ammonia clusters and aqueous ammonia has also been investigated by Auger electron spectroscopy. With those results it was possible to assign a previously observed feature in the Auger electron spectrum of solid ammonia.
|
|
| 20. |
|
|
| 21. |
|
|
| 22. |
- Lundwall, M., et al.
(författare)
-
Neighbor-induced photoelectron recapture in argon clusters : A photon-energy-dependent study of Auger spectra
- 2008
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 78:6, s. 065201-
-
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.
|
|
| 23. |
- Lundwall, Marcus, et al.
(författare)
-
Photon energy dependent intensity variations observed in Auger spectra of free argon clusters
- 2006
-
Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 39:16, s. 3321-3333
-
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.
|
|
| 24. |
- Lundwall, Marcus, et al.
(författare)
-
Preferential site occupancy observed in coexpanded argon-krypton clusters
- 2006
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 74:4, s. 043206-
-
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.
|
|
| 25. |
- Lundwall, Marcus, 1977-
(författare)
-
Rare-gas Clusters Studied by Electron Spectroscopy : Structure of Heterogeneous Clusters and Effects of Electron Scattering on Auger Decay
- 2007
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this Thesis experimental studies of nano-clusters using synchrotron radiation based photoelectron (UPS and XPS) and Auger Electron Spectroscopy (AES) are presented. The investigations may be divided into two parts where the first reports on the structure of heterogeneous two component clusters, and the second concerns electronic decay processes.Using photoelectron spectroscopies as investigative tools the radial composition of heteroclusters of argon mixed with xenon, krypton or neon has been determined. Two methods of heterogeneous cluster production were employed: co-expansion and doping/pick-up. By analyzing the line shapes, energy positions, and widths of the spectral cluster features the radial composition of the clusters produced by co-expansion were found to form close-to-equilibrium structures, placing the component with larger cohesive energy in the cluster core while the second component was to varying degree segregated toward the surface. By instead using the doping/pick-up technique the opposite radial structures, i.e. far-from-equilibrium structures, may be formed. In the case of argon/krypton clusters a similar surface structure is formed regardless of production technique.The second part of the Thesis concerns post-ionization decay processes. Experimental evidence for the Interatomic Coulombic Decay process, a theoretically predicted decay channel, is presented in a study of homogeneous neon clusters. The time scale of the decay was determined to 6±1 fs for bulk atoms and >30 fs for surface atoms in the neon cluster, showing the connection between local geometry and dynamics of the decay.Another channel for electronic relaxation is Auger decay. This Thesis presents a method of disentangling the spectral surface and bulk responses from clusters in Auger spectra. Studies of argon clusters show that the AES technique is more surface sensitive than XPS, even at the same electron kinetic energy. Furthermore, the effect scattering of the photoelectron has on the Auger spectra was investigated. Special effort was put into explaining an experimentally observed photon energy dependent intensity appearing on the high-kinetic energy side on the Auger signal. We propose that this intensity is due to a solid state-specific photoelectron recapture process we name Pre-Auger Recapture (PAR), which affects the kinetic energy of the Auger electrons.
|
|
| 26. |
- Lundwall, Marcus, et al.
(författare)
-
Self-assembled heterogeneous argon/neon core-shell clusters studied by photoelectron spectroscopy
- 2007
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 126:21, s. 214706-
-
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.
|
|
| 27. |
- Mocellin, Alexandra, et al.
(författare)
-
Site selective dissociation upon core ionization of ozone
- 2007
-
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 435:4-6, s. 214-218
-
Tidskriftsartikel (refereegranskat)abstract
- Ozone is found to exhibit substantial site-selective fragmentation when its fragment ions are collected in coincidence with energy selected electrons. We find a preferential production of the O-2(+)/O+(O+/O+) ion pair upon ionization of the terminal (central) oxygen Is electron. Depending on the hole localization, Auger rates are different towards the various final states of the dication, which would produce the observed different fragmentation pattern. We also observe however an increase O-2(+)/O+ production for when the terminal core-hole state is vibrationally excited. This shows the role of the nuclear motion before the Auger decay in the observed site-specific.
|
|
| 28. |
- Ottosson, Niklas, et al.
(författare)
-
An electronic signature of hydrolysation in the X-ray absorption spectrum of aqueous formaldehyde
- 2008
-
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 460:4-6, s. 540-542
-
Tidskriftsartikel (refereegranskat)abstract
- Formaldehyde in aqueous solution is hydrolysed and forms methanediol. Using X-ray absorption spectroscopy we show that the hydrolysation product can be identified by a distinct electronic signature in the spectra. This is manifested by the disappearance of the oxygen 1s -> ; pi* absorption line. The X-ray absorption spectrum of aqueous formaldehyde is compared with those of the structurally similar formamide and urea, which are in contrast not hydrolysed in aqueous solution. We thereby demonstrate the exceptional sensitivity and simplicity of the technique to monitor this fundamental process in the aqueous phase.
|
|
| 29. |
- Ottosson, Niklas, et al.
(författare)
-
Electronic rearrangement upon the hydrolyzation of aqueous formaldehyde studied by core-electron spectroscopies
- 2008
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 112:51, s. 16642-16646
-
Tidskriftsartikel (refereegranskat)abstract
- We have combined near edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS) to study the electronic rearrangement associated with the hydrolyzation of formaldehyde to methanediol in aqueous solution. The spectra are contrasted against those of aqueous formamide and urea, which are structurally similar but do not undergo hydrolysis in solution. We have recently demonstrated that the hydrolyzation of formaldehyde is manifested in the oxygen Is NEXAFS spectrum by the disappearance of the oxygen 1s -> pi* absorption line. This is a characteristic signature that the C=O double bond has been broken. In the present study we extend our investigation to include carbon Is NEXAFS and XPS spectra of the three solutions. The carbon NEXAFS spectra show the C 1s -> pi* absorption line for each solute except for formaldehyde. Moreover, the carbon Is photoelectron spectra exhibit a single peak for each solute. These observations point to a near complete hydrolyzation of formaldehyde, whereas formamide and urea remain intact in the solution. The analysis is further supported by density functional theory (DFT) calculations, showing a C Is chemical shift of approximately 1.0 eV between hydrolyzed and nonhydrolyzed forms, which would give distinguishable features in the photoemission spectrum, if coexisting forms were present in the solutions.
|
|
| 30. |
- Ottosson, Niklas, et al.
(författare)
-
Large variations in the propensity of aqueous oxychlorine anions for the solution/vapor interface
- 2009
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 131:12, s. 124706-
-
Tidskriftsartikel (refereegranskat)abstract
- Core-level photoelectron spectroscopy measurements have been performed of aqueous solutions of NaCl codissolved with NaClOn (n=1-4). Each species has a distinct Cl 2p electron binding energy, which can be exploited for depth-profiling experiments to study the competition between Cl-and ClOn- anions for residing in the outermost layers of the solution/vapor interface. Strongest propensity for the surface is observed for n=4 (perchlorate), followed by n=3 (chlorate), n=2 (chlorite), n=0 (chloride), and n=1 (hypochlorite). Molecular dynamics simulations rationalize the greatest surface propensity of the most oxidized anions in terms of their larger size and polarizability. The anomalous behavior of hypochlorite, being less surface-active than chloride, although it is both larger and more polarizable, is suggested to arise from the charge asymmetry over the anion, increasing its efficiency for bulk solvation. (C) 2009 American Institute of Physics. [doi:10.1063/1.3236805]
|
|
| 31. |
- Peredkov, Sergey, et al.
(författare)
-
Free nanoscale sodium clusters studied by core-level photoelectron spectroscopy
- 2007
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:23, s. 235407-
-
Tidskriftsartikel (refereegranskat)abstract
- Free sodium metal clusters have been studied by probing the Na2p core level using x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The development of electronic structure with size has been studied and discussed in comparison with the atom, dimer, and solid. Information on cluster metallic properties, size, and temperature has been deduced from the XPS measurements. For the large ⟨N⟩>103 Na clusters, the surface and bulk sites have been separated in the photoelectron signal. Auger spectra allowed extracting the information on the valence band. The present study introduces core-level spectroscopies XPS and AES into the field of free neutral metal cluster research.
|
|
| 32. |
|
|
| 33. |
- Peredkov, Sergey, et al.
(författare)
-
Size determination of free metal clusters by core-level photoemission from different initial charge states
- 2007
-
Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121 .- 1550-235X. ; 76:8
-
Tidskriftsartikel (refereegranskat)abstract
- We present the study of free nanoscale lead clusters using photoelectron spectroscopy and synchrotron radiation. Pb 5d core-level spectra reveal the presence of different initial charge states of the clusters created by the magnetron-based source. We suggest a method for determining the cluster size from the charge-dependent core level binding energies. Both the core-level and the valence spectra demonstrate that we have created free metallic clusters with essentially the same electronic structure as the solid.
|
|
| 34. |
- Pokapanich, Wandared, et al.
(författare)
-
Auger Electron Spectroscopy as a Probe of the Solution of Aqueous Ions
- 2009
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 131:21, s. 7264-7271
-
Tidskriftsartikel (refereegranskat)abstract
- Aqueous potassium chloride has been studied by synchrotron-radiation excited core-level photoelectron and Auger electron spectroscopy. In the Auger spectrum of the potassium ion, the main feature comprises the final states where two outer valence holes are localized on potassium. This spectrum exhibits also another feature at a higher kinetic energy which is related to final states where outer valence holes reside on different subunits. Through ab initio calculations for microsolvated clusters, these subunits have been assigned as potassium ions and the surrounding water molecules. The situation is more complicated in the Auger spectrum of the chloride anion. One-center and multicenter final states are present here as well but overlap energetically.
|
|
| 35. |
- Rander, Torbjörn, et al.
(författare)
-
Core-level electron spectroscopy on the sodium dimer Na 2p level
- 2007
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 75:3, s. 032510-
-
Tidskriftsartikel (refereegranskat)abstract
- The lifetime broadening and molecular field splitting of the sodium dimer 2p core level is studied by x-ray photoelectron spectroscopy and by Auger electron spectroscopy. The lifetime of the Na 2p core hole has been determined to be 15±8fs , much shorter than what has previously been reported for solid sodium. The molecular field splitting of this core level has been determined to be 42±10meV . The Auger measurements have experimentally confirmed that the sodium dimer is a good example of when the Coulomb explosion mechanism determines the spectral shape.
|
|
| 36. |
- Rander, Torbjörn, et al.
(författare)
-
Experimental evidence for molecular ultrafast dissociation in O2 clusters
- 2007
-
Ingår i: European Physical Journal D. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 42:2, s. 253-257
-
Tidskriftsartikel (refereegranskat)abstract
- Resonant Auger spectra of O2 clusters excited at the O1s edge are reported. After excitation to the repulsive 1s-13σ* state, the resulting resonant Auger spectrum displays features that remain constant in kinetic energy as the photon energy is detuned. The shift between known atomic fragment features and these features is consistent with that observed for atoms and clusters in singly charged states in direct photoemission. These findings are strong evidence for the existence of molecular ultrafast dissociation processes within the clusters or on their surface.
|
|
| 37. |
- Rander, Torbjörn, 1979-
(författare)
-
Photoelectron Spectroscopy on Atoms, Molecules and Clusters : The Geometric and Electronic Structure Studied by Synchrotron Radiation and Lasers
- 2007
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Atoms, molecules and clusters all constitute building blocks of macroscopic matter. Therefore, understanding the electronic and geometrical properties of such systems is the key to understanding the properties of solid state objects.In this thesis, some atomic, molecular and cluster systems (clusters of O2, CH3Br, Ar/O2, Ar/Xe and Ar/Kr; dimers of Na; Na and K atoms) have been investigated using synchrotron radiation, and in the two last instances, laser light. We have performed x-ray photoelectron spectroscopy (XPS) on all of these systems. We have also applied ultraviolet photoelectron spectroscopy (UPS), resonant Auger spectroscopy (RAS) and near-edge x-ray absorption spectroscopy (NEXAFS) to study many of the systems. Calculations using ab initio methods, namely density functional theory (DFT) and Møller-Plesset perturbation theory (MP), were employed for electronic structure calculations. The geometrical structure was studied using a combination of ab initio and molecular dynamics (MD) methods.Results on the dissociation behavior of CH3Br and O2 molecules in clusters are presented. The dissociation of the Na2 molecule has been characterized and the molecular field splitting of the Na 2p level in the dimer has been measured. The molecular field splitting of the CH3Br 3d level has been measured and the structure of CH3Br clusters has been determined to be similar to the structure of the bulk solid. The diffusion behavior of O2, Kr and Xe on large Ar clusters, as a function of doping rate, has been investigated. The shake-down process has been observed from excited states of Na and K. Laser excited Na atoms have been shown to be magnetically aligned. The shake-down process was used to characterize the origin of various final states that can be observed in the spectrum of ground-state K.
|
|
| 38. |
- Rosso, A., et al.
(författare)
-
Adsorption of polar molecules on krypton clusters
- 2007
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 127:8, s. 084313-084313-5
-
Tidskriftsartikel (refereegranskat)abstract
- The formation process of binary clusters has been studied using synchrotron based core level photoelectron spectroscopy. Free neutral krypton clusters have been produced by adiabatic expansion and doped with chloromethane molecules using the pickup technique. The comparison between the integrated intensities, linewidths, and level shifts of the cluster features of pure krypton and of chloromethane-krypton clusters has been used to obtain information about the cluster geometry. We have shown that most of the chloromethane molecules remain on the surface of the clusters.
|
|
| 39. |
- Rosso, Aldana, 1981-
(författare)
-
Free Molecular and Metal Clusters Studied by Synchrotron Radiation Based Electron Spectroscopy
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main purpose of this Thesis is the experimental characterization of the electronic and geometric structures of objects called clusters. A cluster consists of a finite group of bound atoms or molecules. Due to its finite size, it may present completely different properties than those of the isolated atom and the bulk. The clusters studied in this work are constituted by rare-gas atoms, organic molecules, and metal atoms. Intense cluster beams were created using either an adiabatic expansion source or a gas-aggregation source, and investigated by means of synchrotron radiation based photoelectron spectroscopy. The reports presented in this Thesis may be divided into three parts. The first one deals with results concerning homogeneous molecular clusters (benzene- and methyl-related clusters) highlighting how molecular properties, such as dipole moment and polarizability, influence the cluster structure. The second part focuses on studies of solvation processes in clusters. In particular, the adsorption of polar molecules on rare-gas clusters is studied. It is shown that the doping method, i.e. the technique used to expose clusters to molecules, and the fraction of polar molecules are important factors in determining the location of the molecules in the clusters. Finally, a summary of investigations performed on metal clusters is presented. The applicability of solid state models to analyse the cluster spectra is considered, and the differences between the atomic, cluster and solid electronic structures are discussed.
|
|
| 40. |
- Rosso, Aldana, et al.
(författare)
-
Photoelectron spectroscopy study of free potassium clusters : core level lines and plasmon satellites
- 2008
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 77:4, s. 043202(1)-043202(5)
-
Tidskriftsartikel (refereegranskat)abstract
- Free neutral potassium clusters of two different mean sizes were produced using a gas aggregation source. The K 3p core level was probed by means of synchrotron radiation based photoelectron spectroscopy. The absolute binding energy and the intensity ratio of the surface and bulk spectral features were used to obtain independent estimates of the cluster size. Plasmon satellites in core level spectra of free metallic clusters were observed. Surface and bulk plasmon energies were determined. The interplay between the core line and plasmon integrated intensities is discussed.
|
|
| 41. |
- Rosso, Aldana, et al.
(författare)
-
Synchrotron radiation study of chloromethane clusters : Effects of polarizability and dipole moment on core level chemical shifts
- 2007
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 127:2, s. 024302-
-
Tidskriftsartikel (refereegranskat)abstract
- Free neutral chloromethane clusters have been produced by adiabatic expansion and investigated by means of photoelectron spectroscopy. By studying the differences between the cluster binding energy shifts at the Cl 2p and C 1s thresholds we have shown that antiparallel packing is the dominant local structure of the clusters. This geometry is induced by the polar character of the constituent molecules, and it accords with the structures of chloromethane solids and dimers. Furthermore, results obtained from the analysis of the outer valence levels of the clusters support the suggested local structure. The roles of the polarizability and of the dipole moment of the constituent molecules in the cluster binding energy shifts are discussed in comparison with a recent investigation of bromomethane clusters.
|
|
| 42. |
- Rosso, Aldana, et al.
(författare)
-
The role of molecular polarity in cluster local structure studied by photoelectron spectroscopy
- 2007
-
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 435:1-3, s. 79-83
-
Tidskriftsartikel (refereegranskat)abstract
- We have studied the spatial structure and electronic levels of clusters of the molecule CH3Br to investigate the effects of molecular polarity on these properties. Analysis of the core level photoelectron spectra of initially neutral CH3Br clusters shows that the C 1 s-1 state has a 30% larger binding energy shift between free molecules and clusters than the Br 3d-1 state. This difference is attributed to an anti-parallel packing of the molecules induced by the polar character of bromomethane. The results obtained from the analysis of valence cluster spectra also support the proposed structure.
|
|
| 43. |
- Rosso, Aldana, et al.
(författare)
-
The valence band of free K clusters studied by photoelectron and Auger spectroscopies
- 2008
-
Ingår i: European Physical Journal D. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 50:2, s. 165-169
-
Tidskriftsartikel (refereegranskat)abstract
- The valence states of free neutral potassium clusters produced by a gas aggregation source were probed by synchrotron radiation based photoelectron spectroscopy. The first ionization energy (IE) of the clusters was determined to be 10% larger than the work function of bulk potassium. Using electrostatic concepts and the IE, the mean size of the clusters was estimated to be ≈2000 atoms. Further information about the valence band was provided by investigation of the Auger process initiated by the ionization of the 3p level with a subsequent emission of an Auger electron from the valence band (M2,3VV). Plasmon satellites were observed in Auger spectra of free metal clusters.
|
|
| 44. |
|
|
| 45. |
- Tchaplyguine, Maxim, et al.
(författare)
-
Absolute core-level binding energy shifts between atom and solid: The Born-Haber cycle revisited for free nanoscale metal clusters
- 2008
-
Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 166, s. 38-44
-
Tidskriftsartikel (refereegranskat)abstract
- Core-level binding energy shifts between the free atom and corresponding large clusters, the latter closely approximating the infinite solid, have been experimentally derived for several elemental metals. The cluster core-level binding energies in question have been determined relative to the vacuum level using synchrotron-based photoelectron spectroscopy. As expected, the experimental shift values show reasonable agreement with those calculated using the thermochemical Born–Haber cycle approach. The largest uncertainty factors defining the discrepancies between the experiment and the model, such as the difference in the multiplet structure of free atoms and the solid, the in some cases indirectly established cluster work functions, and the metal solvation energy, are discussed.
|
|
| 46. |
- Tchaplyguine, Maxim, et al.
(författare)
-
Direct observation of the non-supported metal nanoparticle electron density of states by X-ray photoelectron spectroscopy
- 2007
-
Ingår i: European Physical Journal D. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 45:2, s. 295-299
-
Tidskriftsartikel (refereegranskat)abstract
- Synchrotron-based X-ray photoelectron spectroscopy on copper and silver cluster beams created by a magnetron-based gas-aggregation source has allowed mapping the electron density of states (DOS) of free metallic nanoparticles. The cluster DOS profiles obtained in the experiments strongly resemble the infinite solid DOS shapes, but the extracted cluster work-functions are lower than those for the bulk metal. The latter observation is explained by the initial negative charge on most of the clusters, created by the source.
|
|
| 47. |
- Tchaplyguine, Maxim, et al.
(författare)
-
Localized versus delocalized excitations just above the 3d threshold in krypton clusters studied by Auger electron spectroscopy
- 2007
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 127:12, s. 124314-
-
Tidskriftsartikel (refereegranskat)abstract
- We present Auger spectroscopy studies of large krypton clusters excited by soft x-ray photons with energies on and just above the 3d(52) ionization threshold. The deexcitation spectra contain new features as compared to the spectra measured both below and far above threshold. Possible origins of these extra features, which stay at constant kinetic energies, are discussed: (1) normal Auger process with a postcollision interaction induced energy shift, (2) recapture of photoelectrons into high Rydberg orbitals after Auger decay, and (3) excitation into the conduction band (or "internal" ionization) followed by Auger decay. The first two schemes are ruled out, hence internal ionization remains the most probable explanation.
|
|
| 48. |
|
|
| 49. |
|
|
| 50. |
- Winter, B., et al.
(författare)
-
Hydrogen bonding in liquid water probed by resonant Auger-electron spectroscopy
- 2007
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 127:9, s. 094501-094501-6
-
Tidskriftsartikel (refereegranskat)abstract
- We have measured resonant and off-resonant Auger-electron spectra of liquid water. Continuumlike transitions near and above the O1s vertical ionization energy are identified by the characteristic normal Auger-electron spectra. On the contrary, well-resolved spectator shifts of the main Auger-electron peak are observed at the liquid-water O1s absorption main edge and near the absorption pre-edge. The shifts of 1.4 and 1.9 eV arise from the localized nature of the excitation. Excited-state localization/delocalization is also discussed for the analogous vacuum ultraviolet (VUV) transitions, and we point out the similarities between x-ray and VUV absorption spectra of liquid water.
|
|
