Experimental study of photoionization of ozone in the 12 to 21 eV region

The total and partial ion yield of ozone using time-of-flight is presented. The measurements were done using multicoincidence between a photoelectron and a photoion (PEPICO). Comparison with the photoelectron spectrum and previous measurements using other techniques allowed the assignment of most broad features in the spectra. Kinetic energy released is obtained for O+ and O-2(+) ions. A discussion about the dissociation channels is included. (C) 2001 American Institute of Physics.115115041504

Structural analysis of Pt(1 1 1)c(√3 × 5)rect.–CO using photoelectron diffraction

Core level shift scanned-energy mode photoelectron diffraction using the two distinct components of the C 1s emission has been used to determine the structure of the Pt(1 1 1)c(√3 × 5)rect.–CO phase formed by 0.6 ML of adsorbed CO. The results confirm earlier assignments of these components to CO in atop and bridging sites, further confirm that the best structural model involves a 2:1 occupation ratio of these two sites, and provides quantitative structural parameter values. In particular the Pt–C chemisorption bondlengths for the atop and bridging sites are, respectively, 1.86 ± 0.02 Å and 2.02 ± 0.04 Å. These values are closely similar to those found in the 0.5 ML coverage c(4 × 2) phase, involving an atop:bridge occupation ratio of 1:1, obtained in earlier quantitative low energy electron diffraction studies. The results also indicate a clear tilt of the molecular axis of atop CO species in this compression phase, consistent with the finding of an earlier electron-stimulated desorption ion angular distribution investigatio

Plasmon single- and multi-quantum excitation in free metal clusters as seen by photoelectron spectroscopy.

Plasmons are investigated in free nanoscale Na, Mg, and K metal clusters using synchrotron radiation-based x-ray photoelectron spectroscopy. The core levels for which the response from bulk and surface atoms can be resolved are probed over an extended binding energy range to include the plasmon loss features. In all species the features due to fundamental plasmons are identified, and in Na and K also those due to either the first order plasmon overtones or sequential plasmon excitation are observed. These features are discussed in view of earlier results for planar macroscopic samples and free clusters of the same materials

Probing aqueous ions with non-local Auger relaxation

Non-local analogues of Auger decay are increasingly recognized as important relaxation processes in the condensed phase. Here, we explore non-local autoionization, specifically Intermolecular Coulombic Decay (ICD), of a series of aqueous-phase isoelectronic cations following 1s core-level ionization. In particular, we focus on Na+, Mg2+, and Al3+ ions. We unambiguously identify the ICD contribution to the K-edge Auger spectrum. The different strength of the ion-water interactions is manifested by varying intensities of the respective signals: the ICD signal intensity is greatest for the Al3+ case, weaker for Mg2+, and absent for weakly-solvent-bound Na+. With the assistance of ab initio calculations and molecular dynamics simulations, we provide a microscopic understanding of the non-local decay processes. We assign the ICD signals to decay processes ending in two-hole states, delocalized between the central ion and neighbouring water. Importantly, these processes are shown to be highly selective with respect to the promoted water solvent ionization channels. Furthermore, using a core-hole-clock analysis, the associated ICD timescales are estimated to be around 76 fs for Mg2+ and 34 fs for Al3+. Building on these results, we argue that Auger and ICD spectroscopy represents a unique tool for the exploration of intra- and inter-molecular structure in the liquid phase, simultaneously providing both structural and electronic information

Photoelectron diffraction: from phenomenological demonstration to practical tool

The potential of photoelectron diffraction—exploiting the coherent interference of directly-emitted and elastically scattered components of the photoelectron wavefield emitted from a core level of a surface atom to obtain structural information—was first appreciated in the 1970s. The first demonstrations of the effect were published towards the end of that decade, but the method has now entered the mainstream armoury of surface structure determination. This short review has two objectives: First, to outline the way that the idea emerged and the way this evolved in my own collaboration with Neville Smith and his colleagues at Bell Labs in the early years: Second, to provide some insight into the current state-of-the art in application of (scanned-energy mode) photoelectron diffraction to address two key issue in quantitative surface structure determination, namely, complexity and precision. In this regard a particularly powerful aspect of photoelectron diffraction is its elemental and chemical-state specificity

Ultrafast charge delocalization dynamics in aqueous electrolytes: New insights from Auger electron spectroscopy

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 processes can be probed using Auger electron spectroscopy. The use of the core-hole clock method to extract dynamical information from Auger spectra is described. By a number of examples we demonstrate how the efficiency for ultrafast charge transfer phenomena on the low femtosecond timescale is determined not only by factors such as charge, polarizability and solvated radius of the ionic solutes but also by the dominant interactions of the ionized site with its surroundings in the intermediate state. (C) 2012 Elsevier B.V. All rights reserved

Tuning the oxidation degree in sub-10 nm silver-oxide nanoparticles: From Ag2O monoxide to AgOx(x > 1) superoxide

A preparation method for silver-oxide containing nanoparticles is described. The suggested approach allows varying the oxidation degree from monoxide to an oxygen-rich state resembling superoxide The method is based on magnetron reactive sputtering and vapour aggregation, and utilizes silver-oxygen interaction in the vapour phase - prior to the nanoparticle aggregation from the vapour. Synchrotron-based photoelectron spectroscopy - a local probing method with high chemical sensitivity - allows 'on-the-fly' analysis of the composition and oxidation degree in nanoparticles, before any deposition of the particles. Preparation and properties of oxygen-rich nanoparticles are discussed in connection to the catalytic processing of economically important hydrocarbons. (C) 2014 Elsevier B.V. All rights reserved

Size-varied photoelectron spectroscopy of metal clusters using the Exchange Metal Cluster Source

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

Charge delocalization dynamics of ammonia in different hydrogen bonding environments: free clusters and in liquid water solution

Valence and core level photoelectron spectra and Auger electron spectra of ammonia in pure clusters have been measured. The Auger electron 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, hydrogen 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