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We review the basic principles of ultrafast charge delocalization phenomena in aqueous electrolytes following core-level photoionization and resonant core-level excitations, and describe how these ...

Electronic structure of free and neutral Rb and K clusters containing from few tens to few hundred atoms has been studied using synchrotron radiation. Core-level photoelectron spectroscopy has been used to probe the metallic nature of Rb and K clusters. We show that the metallicity exists down to the dimensions of few nanometers. Simultaneously the emergence and evolution of the valence band structure has been monitored by the valence-level photoelectron spectroscopy.

In this paper we present the first core-level photoelectron spectroscopic study of solid nanoparticles in liquid water. The particles are SiO(2)-based with an average diameter of 70 nm and function ...

By a combination of surface-sensitive photoelectron spectroscopy and molecular dynamics simulations, we characterize the surface propensity of the iodide anion in aqueous solutions at acidic, neutral, and basic conditions (pH = 1, 6.8 and 13). In both experiments and simulations, an increased surface concentration of I- is found in non-neutral solutions. We interpret these findings in terms of I- surface coadsorption with hydronium at low pH and "salting out" of iodide by hydroxide from the bulk solution to the surface at high pH. The present study is thus in accord with the picture of a weak surface adsorption of hydronium and surface depletion of hydroxide, being in sharp contradiction with the interpretation of electrophoretic and titration measurements in terms of strong surface enrichment of OH-.

The 2s and 2p photoelectron spectra have been measured for Na(+), Mg(2+), and Al(3+) ions in aqueous solution. In all cases, the 2s lines are significantly broader than the 2p features, which is attributed to a shorter lifetime of the respective 2s hole. Since intraionic Coster-Kronig decay channels from the (2s)(-1) state are closed for free Na(+), Mg(2+), and Al(3+) ions, this is evidence for an intermolecular Coster-Kronig-like process, reminiscent of intermolecular Coulombic decay (ICD), involving neighboring water solvent molecules. The observed 2s Lorentzian line widths correspond to lifetimes of the (2s)(-1) state of 3.1, 1.5, and 0.98 fs for the solvated Na, Mg, and Al ions, respectively.

The recently developed Exchange Metal Cluster Source (EXMEC) is described. The source is designed for electron-spectroscopic studies of neutral metal clusters. Preliminary results on the rubidium and tin clusters using synchrotron radiation excited photoelectron spectroscopy show the capability for cluster production in the size regime of few tens to few hundred of atoms per cluster. A wide range of metal evaporation temperatures is covered applying resistive and induction heating methods. (C) 2010 Elsevier B.V. All rights reserved.

This paper reports the characteristics and performance of a Time-of-Flight Mass Spectrometer (TOF-MS) for coincidence measurements between electrons and ions that has been developed jointly in Sweden and Brazil. The spectrometer, used for studies of inner-shell photoexcitation of molecules in the gas-phase, has been optimized by implementing ion and electron lenses to allow the use of relatively small diameter detectors. Simulations were performed to understand the lens performance and they show that ions (electrons) could be collected without angular discrimination with a maximum kinetic energy up to ten (two) times higher than without the lens actions. A rotary vacuum chamber allows the spectrometer axis to be positioned at different angles relative to the polarization vector of the excitation beam. An important characteristic of the apparatus is that the acquisition setup allows a multi-hit capability with 1 ns resolution. Hereby, Photoelectron-Photoion-Photoion Coincidence (PEPIPICO) measurements can be performed on molecules containing two or more atoms of equal mass. A method to obtain experimental detection efficiencies of a single ion and one of one, two or three electrons has been developed. A systematic study of the interaction region has been performed to determine the shape of the photon and gas beams. Measurements on molecular nitrogen demonstrate the spectrometer's ability to resolve fragments with the same charge to mass ratio arriving within only a few ns. Simulations and experimental results of fragmentation of two singly charged cation nitrogen atoms agree, confirming that the spectrometer performance is well understood. (C) 2010 Elsevier B.V. All rights reserved.

Surface affinity of aqueous guanidinium chloride (GdmCl) is compared to that of aqueous tetrapropylammonium chloride (TPACl) upon addition of sodium chloride (NaCl) or disodium sulfate (Na2SO4). The experimental results have been acquired using the surface sensitive technique X-ray photoelectron spectroscopy on a liquid jet. Molecular dynamics (MD) simulations have been used to produce radial distribution functions and surface density plots. The surface affinities of both TPA+ and Gdm+ increase upon adding NaCl to the solution. With the addition of Na2SO4 the surface affinity of TPA+ increases while that of Gdm+ decreases. From the results of MD simulations it is seen that Gdm+ and SO4^2- ion pairs. This finding can be used to explain the decreased surface affinity of Gdm+ when co-dissolved with SO4^2- ions. Since SO4^2- ions avoid the surface due to the double charge and strong water interaction, the Gdm+-SO4^2- ion pair resides deeper in the solutions' bulk than the Gdm+ ions. Since TPA+ does not form ion pairs with SO4^2- the TPA+ ions are instead enriched at the surface.

Nitrogen and oxygen K emission spectra of glycine in the form of anions, zwitterions, and cations in aqueous solution are presented. It is shown that protonation has a dramatic influence on the local electronic structure and that the functional groups give a distinct spectral fingerprint.

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-a-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.

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.

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 ...

Auger spectra from the decay of core-ionized N-2 have been studied as a function of the exciting photon energy. Discrete features appear in the Auger spectrum when the photon energy is tuned to the shape-resonance region at 420 eV. The Auger spectra for two final dicationic states are studied; simulations of the contributions from the decay of the gerade and ungerade core-hole states are made based on a Franck-Condon picture including life time vibrational interference. We are able to reproduce the vibrational. ne structure in the Auger spectrum using a model where the coherent sum of the decay channels from the vibrationally-excited states are treated separately for the gerade and ungerade states.

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.

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 cons ...

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. (c) 2007 Elsevier B.V. All rights reserved.

The acid-base speciation of surface-active carboxylate ions in the surface region of aqueous solutions was studied with synchrotron-radiation-based photoelectron spectroscopy. The protonated form was found at an extraordinarily large fraction compared to that expected from the bulk pH. When adding salts containing the weak acid NH4(+) to the solution, the fraction of the acidic form at the surface increases, and to a much greater extent than expected from the bulk pH of the solution. We show that ammonium ions also are overrepresented in the surface region, and propose that the interaction between the surface-active anionic carboxylates and cationic ammonium ions creates a carboxylate-ammonium bilayer close to the surface, which increases the probability of the protonation of the carboxylate ions. By comparing the situation when a salt of the less volatile amine diethanolamine is used, we also show that the observed evaporation of ammonia that occurs after such an event only affects the equilibrium marginally.

Position isomerism is ubiquitous in atmospheric oxidation reactions. Therefore, we have compared surface-active oxygenated amphiphilic isomers (1- and 3-pentanol) at the aqueous surface with surface- and chemically sensitive X-ray photoelectron spectroscopy (XPS), which reveals information about the surface structure on a molecular level. The experimental data are complemented with molecular dynamics (MD) simulations. A concentration-dependent orientation and solvation of the amphiphiles at the aqueous surface is observed. At bulk concentrations as low as around 100 mM, a monolayer starts to form for both isomers, with the hydroxyl groups pointing towards the bulk water and the alkyl chains pointing towards the vacuum. The monolayer (ML) packing density of 3-pentanol is approx. 70% of the one observed for 1-pentanol, with a molar surface concentration that is approx. 90 times higher than the bulk concentration for both molecules. The molecular area at ML coverage (approximate to 100 mM) was calculated to be around 32 +/- 2 angstrom(2) per molecule for 1-pentanol and around 46 +/- 2 angstrom(2) per molecule for 3-pentanol, which results in a higher surface concentration (molecules per cm(2)) for the linear isomer. In general we conclude therefore that isomers - with comparable surface activities - that have smaller molecular areas will be more abundant at the interface in comparison to isomers with larger molecular areas, which might be of crucial importance for the understanding of key properties of aerosols, such as evaporation and uptake capabilities as well as their reactivity.

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.

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.

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.

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.

Theoretical models of lineshapes in Ar2p photoionization spectra have been calculated for free, neutral argon clusters of different sizes. The lineshape models are fitted to experimental spectra and used to estimate the mean cluster size realized in the experiment. The results indicate that size estimators working from stagnation conditions [R. Karnbach, M. Joppien, J. Stapelfeldt, J. Wörmer and T.Möller, Rev. Sci. Instrum., 1993, 64, 2838] may underestimate the mean cluster size.

We address the influence of clustering on the ultra-fast dissociation of bromomethane. Valence and core photo-electron spectroscopy, partial electron yield absorption, and resonant Auger spectroscopy have been used together with ab initio calculations to investigate the properties of the ultra-fast dissociation. The ratio of ultra-fast dissociation of molecules in clusters as compared to free molecules is determined to be significantly reduced. We propose partial delocalization of the excited electronic state as being responsible for this behavior. UBJL

The surface-to-bulk intensity ratio in Auger electron spectra has been studied in comparison with core-level photoelectron spectra using free argon clusters of sizes ranging over two orders of magnitude. Enhanced surface sensitivity is observed in L2,3M2,3M2.3 Auger electron spectra compared to 2p photoelectron spectra where electrons of similar kinetic energies were recorded. This is discussed in terms of the effective attenuation length of the electrons.

We present new results for the inner valence levels of clusters of the three inert gases Ar, Kr and Xe based on photoelectron spectroscopy studies. The inner valence levels are compared to the localised core levels and to the delocalised outer valence levels. This comparison shows a gradual change from a relatively localised behaviour for Ar inner valence 3s, over the intermediate case of Kr inner valence 4s, to a more delocalised behaviour for Xe inner valence 5s. This change correlates well with the ratio between the orbital sizes and the interatomic distances. The Kr4s intermediate case is found to exhibit characteristics of both localised and delocalised behaviour.

An in-depth photoionization study of the inner-valence electrons in HCl and DCl has been performed using synchrotron radiation. A series of photoelectron spectra of HCl were obtained at a resolution of 23 meV over the binding energy range 25-30.5 eV at various excitation energies and at two different electron collection angles relative to the plane of polarization of the undulator radiation. In addition, photoelectron spectra of DCl were recorded at two different excitation energies. These spectra were compared directly with the threshold photoelectron spectra of HCl and DCl that were recorded previously under similar resolution conditions (similar to30 meV). This comparative study reveals new information on the nature of the numerous band systems observed in this binding energy region. In addition, we present the experimental confirmation of the theoretical prediction given by Andersson et al (2001 Phys. Rev. A 65 012705) that a vibrational progression showing interference structure would appear in the main inner-valence ionization band in the photoelectron spectrum of DCl at a resolution of 10 meV.

The N 1s --> pi* photoabsorption profile of N-2 is quantitatively analysed. New spectroscopical constants for the N 1s(-1) pi* core-excited state are determined from NEXAFS spectra and compared to previously published data. The accuracy of the new spectroscopical constants is discussed and error bars are given for the present data analysis. The goodness of the new spectroscopical constants is demonstrated by lifetime vibrational interference (LVI) simulations of the resonant Auger decay from the N 1s(-1) pi* core-excited state to the A(2)Pi(u) singly ionized final state of N-2. These new values give a much better agreement with recently obtained experimental data compared to the previously published ones.

We show that the undular stray light, diffusely scattered by the optical system of a synchrotron beamline, can play an important role in the formation of high-resolution resonant photoelectron (RPE) spectra. The influence of the stray light is mediated through the Stokes doubling effect, with the Lorentzian tail of the spectral function being replaced by a more complicated form. This effect is shown to appear in the high-resolution resonant photoelectron spectrum of the N-2 molecule in which the spectral shape of the "non-Raman (NR) bands" differs qualitatively for the A(2)Pi(u) and X(2)Sigma(g)(+) final states. A particularly large enhancement of the non-Raman Stokes line is observed for the A-state while the picture is inverted for the X-state where the non-Raman band is suppressed. It is shown that the resonant photoemission profile is affected by two qualitatively different detunings, the detuning of the monochromatized line relative to the photoabsorption line and the detuning of the undulator harmonic relative to the same reference line. The experimental data show that the relative intensity of the non-Raman line strongly depends on the tuning of the undulator harmonic with respect to the selected monochromator bandpass, leading to a strong decrease of the Stokes line intensity for certain undulator detunings. A clear red-shift asymmetry for the decrease in the Stokes line intensity is observed when the monochromator line is detuned towards negative photon frequencies, whereas the picture is reverted for the situation of a positively detuned monochromator line. The results show the necessity to control the stray light and to investigate both the Raman and non-Raman contributions to the spectral profiles in order to avoid misinterpretation and in order to make full use of the information available in resonant photoemission spectra of molecules.

We report an observation of substantial deviations in the photoelectron angular distribution for photoionization of atoms in free Xe clusters compared to the case of photoionization of free atoms. The cross section, however, seems not to vary between the cluster and free atoms. This observation was made in the vicinity of the Xe 4d Cooper minimum, where the atomic angular distribution is known to vary dramatically. The angular distribution of electrons emitted from atoms in the clusters is more isotropic than that of free atoms over the entire kinetic energy range studied. Furthermore, the angular distribution is more isotropic for atoms in the interior of the clusters than for atoms at the surface. We attribute this deviation to elastic scattering of the outgoing photoelectrons. We have investigated two average cluster sizes, (N) approximate to 4000 and 1000 and found no significant differences between these two cases. (Less)

In this paper the first resonant photoemission and partial electron yield studies of free clusters are presented. The resonant photoemission spectra of free argon clusters have been recorded with excitation energies determined from the cluster X-ray absorption spectrum near the Ar 2p ionization threshold. The decay of 2p(-1)4s and 2p(-1)3d cluster surface and "bulk" excited states has been investigated in detail. The combination of resonant photoemission and partial electron yield methods has allowed a selective probing of the electronic and geometric structure, yielding new results concerning the interplay between the energy of the excited states, their orbital character and the local atomic coordination. These new results demonstrate the power of resonant core level spectroscopy when applied to free clusters, as well as the advantages of free clusters for the studies of the bulk and surface energetics of nanoscale solids. (C) 2002 Elsevier Science B.V. All rights reserved. (Less)

We show that frequency detuning in a resonant X-ray scattering experiment acts as an X-ray camera shutter by regulating the duration time of the scattering process. The camera shutter can be used to select processes at different time scales for observation. This is illustrated by a resonant Auger study of the ultra-fast dissociation of the core-excited HF molecule. We present experimental results and first principle simulations of the molecular fraction in the resonant Auger spectra of HF which is a dynamical parameter that well illustrates X-ray shutter controlled dissociation.

We present evidence for ultra-fast dissociation of molecular ammonia when photo-excited to the Nls --> 4a(1) core-hole state. This finding is based on resonant Auger spectroscopical results as well as qualitative arguments concerning the photon energy dependence of the Auger structures. Calculations of the excited state potential based on the Z + l approximation were performed. Both the calculations and the measurements indicate that the most likely fragmentation pathway for the core excited ammonia molecules leads to NH2* and H fragments. (C) 2003 Elsevier Science B.V. All rights reserved.

The Auger–Doppler effect in the experimental spectra of HF and DF is presented, and the dynamics of ultra-fast dissociation in the core-excited state are discussed. The Doppler splitting of the atomic Auger peak is calculated and simulated using a classical model and a very good agreement is found between experiment and simulation. It is shown that the difference in photon energy relative to the resonance is transferred completely into the kinetic energy release (KER). This is expected to be a general phenomenon, but is clearly illuminated in the HF/DF case. Thus the fragment velocity can be controlled through photon energy detuning.

Core level spectroscopy offers probing of atomic matter localized both in time and space. The temporal localization is due to the short lifetime of core holes, which opens a window from the energy domain to the low femtosecond time domain. The thus enabled studies of dynamic phenomena are exemplified by ultrafast dissociation of molecules. It is shown how information may be obtained about a characteristic dissociation time scale and the fragment velocities. The latter are also shown to be photon-energy-dependent. The spatial localization is due to the atomic character of core levels even in polyatomic systems. Clusters have a high and size-dependent fraction of atoms at the surface, and this leads to size-dependent properties. The spatially local character of core level spectroscopy is shown to be very valuable for separating contributions from surface and bulk atoms in free clusters.

The water-vapor interface of aqueous solutions of succinic acid, where pH values and bulk concentrations were varied, has been studied using surface sensitive X-ray photoelectron spectroscopy (XPS) and molecular dynamics (MD) simulations. It was found that succinic acid has a considerably higher propensity to reside in the aqueous surface region than its deprotonated form, which is effectively depleted from the surface due to the two strongly hydrated carboxylate groups. From both XPS experiments and MD simulations a strongly increased concentration of the acid form in the surface region compared to the bulk concentration was found and quantified. Detailed analysis of the surface of succinic acid solutions at different bulk concentrations led to the conclusion that succinic acid saturates the aqueous surface at high bulk concentrations. With the aid of MD simulations the thickness of the surface layer could be estimated, which enabled the quantification of surface concentration of succinic acid as a multiple of the known bulk concentration. The obtained enrichment factors were successfully used to model the surface tension of these binary aqueous solutions using two different models that account for the surface enrichment. This underlines the close correlation of increased concentration at the surface relative to the bulk and reduced surface tension of aqueous solutions of succinic acid. The results of this study shed light on the microscopic origin of surface tension, a macroscopic property. Furthermore, the impact of the results from this study on atmospheric modeling is discussed.

We present synchrotron-based I4d photoelectron spectroscopy experiments of solutions from LiI and LiI3 in water, ethanol, and acetonitrile. The experimentally determined solvent-induced binding energy shifts (SIBES) for the monatomic I(–) anion are compared to predictions from simple Born theory, PCM calculations, as well as multiconfigurational quantum chemical spectral calculations from geometries obtained through molecular dynamics of solvated clusters. We show that the SIBES for I(–) explicitly depend on the details of the hydrogen bonding configurations of the solvent to the I(–) and that static continuum models such as the Born model cannot capture the trends in the SIBES observed both in experiments and in higher-level calculations. To extend the discussion to more complex polyatomic anions, we also performed experiments on I3(–) and I(–)/I3(–) mixtures in different solvents and the results are analyzed in the perspective of SIBES. The experimental SIBES values indicate that the solvation effects even for such similar anions as I(–) and I3(–) can be rather different in nature.

Core-shell-structured nanoalloy particles with an Al-dominated interior covered by few Yb monolayers have been fabricated using a vapor-aggregation method involving magnetron sputtering. The radially segregated structure of the Yb-Al nanoparticles has been disclosed by "on-the-fly" photoelectron spectroscopy monitoring of the nanoparticle beam in Yb 4f and Al 2p electron binding energy regions. Both, the binding energy values and the electron microscopy images taken on the deposited nanoparticles, allow estimating their dimensions to be in the 5-10 nm range. The photoelectron spectroscopy results suggest that in these nanoparticles no trivalent Yb - the typical case for the macroscopic Yb-Al alloy - is present. The oxidation of preformed Yb-Al nanoparticles was successfully attempted, leading to the appearance of divalent Yb surface oxide - in contrast to the bulk macroscopic Yb which is trivalent in the oxide. Our results suggest that at intermediate oxygen exposures "sandwich-like" nanoparticles of YbO/Yb/Al were synthesized. At higher O2 exposures, the oxygen seems to penetrate all the way to the Yb-Al interface. The results of the present study have to be considered when photonic applications of Yb-doped garnet nanoparticles are planned.

Resonant excitation to the F1s-σ* dissociative state in hydrogen fluoride gives a photoelectron spectrum where the spectator part contains strong atomic lines but a participator part where such lines are lacking. We demonstrate that this contrasting behaviour between the two parts is due to a strong dynamical suppression of the resonant contribution, making direct main state photoionization the dominating channel even at resonant conditions.

Free bare gold clusters in the size range from few tens to few hundred atoms (≤1 nm dimensions) have been produced in a beam, and the size-dependent development of their full valence band including the 5d and 6s parts has been mapped 'on the fly' by synchrotron-based photoelectron spectroscopy. The Au 4f core level has been also probed, and the cluster-specific Au 4f ionization energies have been used to estimate the cluster size. The recorded in the present work valence spectra of the small clusters are compared with the spectra of the large clusters ( N ∼ 103) created by us using a magnetron-based gas aggregation source. The comparison shows a substantially narrower 5d valence band and the decrease in its splitting for gold clusters in the size range of few hundred atoms and below. Our DFT calculations involving the pseudopotential method show that the 5d band width of the ground state increases with the cluster size and by the size N = 20 becomes comparable with the experimental width of the valence photoelectron spectrum. Similar to the earlier observations on supported clusters we interpret our experimental and theoretical results as due to the undercoordination of a large fraction of atoms in the clusters with N ∼ 102 and below. The consequences of such electronic structure of small gold clusters are discussed in connection with their specific physical and chemical properties related to nanoplasmonics and nanocatalysis. (Less)

We have developed an experimental setup for the study of small mass-selected clusters delivered by soft landing to a model oxide support. An automated deposition system to achieve accurately quantified homogeneous surfaces is described which also overcomes beam instability. Finally we present some recent photoelectron spectroscopic data from the analysis of mass-selected Agn+ clusters deposited on a Xe covered Al2O3 surface. Large core-level binding energy shifts are observed as a function of deposited cluster size and diffusion/agglomeration within the noble gas layer.

We employ a pump–probe approach to molecular photoionization to study fast dissociation of Rydberg states in acetylene. By using time-resolved photoelectron spectroscopy to study the electronic state of the resulting ions we are able to monitor the system continuously during dissociation or rearrangement. We find that the predissociative lifetime for the 3R′′′ (v2′=1) Rydberg state is about 150 fs. We demonstrate a powerful new technique using time-correlated femtosecond harmonic generation and laser light pulses to study the time evolution of ultrafast dynamic processes in molecules.

We report the observation of the unusually weak decay of the N 1s --> pi* core-excited N-2 molecule to the (B) over tilde (2)Sigma(u)(+) final state of N-2(+), which is only detectable in an exp ...

By exploiting the core-excitation-induced dissociation of O2, we find that the Auger emission exhibits a Doppler-like energy shift. We show this to be a manifestation of localization of the core hole and propose that the problem of core-hole localization versus delocalization in core-hole spectroscopies may be resolved by considering the nature of the measurement.

The fragmentation of the water molecule upon resonant core excitation and subsequent Auger decay has been studied by electron–ion coincidence spectroscopy. A qualitative comparison between the fragmentation patterns for H 2 O and D 2 O reveals that the anti-bonding nature of the core-excited (*) intermediate state causes appreciable dissociation of the H 2 O* (D 2 O*) into HO*+H (DO*+D) during the lifetime (3.3 fs) of the O1s core hole. A `core–hole clock' model is used to derive approximate quantitative values for the characteristic dissociation time of the core-excited water molecule. The results demonstrate how such a procedure is useful for quantitative experiments with a very high degree of spatial and temporal localization.

Core level x-ray absorption and photoemission spectra of free water clusters are presented. Core and valence photoemission spectra show a weak but gradual change with cluster size. Comparisons to spectra of the isolated molecule and solid ice indicate that water molecules have a lower average coordination in clusters than in the bulk solid. X-ray absorption spectra reveal spectral characteristics between the free molecule and the bulk. These are compared to similar spectra of the isolated molecule and solid ice, and discussed in connection to calculated structures.

We report on the build-up of the new undulator beam line 1411 at the third-generation synchrotron radiation facility MAX II in Lund, Sweden. This beam line is based on an upgraded version of the modified SX700-monochromator and the end station which were installed previously at beam line 51 at MAX I. The end station is equipped with a rotatable Scienta hemispherical electron-analyser making angle-resolved high resolution electron spectroscopy possible for various kinds of samples. The beam line performance will be considerably improved on MAX II due to a new undulator and the superior light source properties, e.g. the small vertical electron beam size. Undulator spectra have been measured and estimates of the photon flux at the experiment and the expected energy resolution are presented. The parameters for a new refocusing mirror were defined by ray tracing using the beam waist of the undulator. The beam line length was extended by 1 m to offer additional space for exchangeable experimental chambers. © 1999 Elsevier Science B.V. All rights reserved.

Auger decay from the C s core-excited state of CO has been studied by means of angular resolved vibrationally selective electron spectroscopy. It is observed that the so-called strict spectator model provides only a qualitative description of the C Auger decay. We interpret this as evidence for a strong valence character of the 3s orbital. Transitions assigned to the Auger shake-up are revealed. For transitions to the final state with s leading configuration, there are indications of angular asymmetry which depend upon the vibrational level of the final state.

The creation and decay of photon-excited Xe 4d5/2,3/2-1 core-hole states has been studied in the photon energy region 70-110 eV, where photon absorption is dominated by the strong shape resonance. Unprecedented experimental quality has enabled the study of nearly inherent Auger electron lineshapes. Analysis on the basis of a post-collision interaction model allows the first ever experimental verification that the Xe 4d5/2,3/2-1 lifetime widths clearly show dynamic, photon-energy-dependent behaviour.

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 → π* 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.