C60_{60} in intense femtosecond laser pulses: nonlinear dipole response and ionization

We study the interaction of strong femtosecond laser pulses with the C$_{60}$ molecule employing time-dependent density functional theory with the ionic background treated in a jellium approximation. The laser intensities considered are below the threshold of strong fragmentation but too high for perturbative treatments such as linear response. The nonlinear response of the model to excitations by short pulses of frequencies up to 45eV is presented and analyzed with the help of Kohn-Sham orbital resolved dipole spectra. In femtosecond laser pulses of 800nm wavelength ionization is found to occur multiphoton-like rather than via excitation of a ``giant'' resonance.Comment: 14 pages, including 1 table, 5 figure

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

Photon Energy Dependent Valence Band Response of Metallic Nanoparticles

We show that the valence band response to photon impact in metallic nanoparticles is highly energy dependent. This is seen as drastic variations of cross sections in valence photoionization of free and initially charge-neutral nanosized metal clusters. The effect is demonstrated in a combined experimental and theoretical study of Rb clusters. The experimental findings are interpreted theoretically using a jellium model and superatom description. The variations are attributed to the changing overlap with the photon energy between the wave functions of diffuse delocalized valence electrons and continuum electrons producing a series of minima in the cross section

Ag-oxide signature in Ag 3d photoelectron spectra : A study on free nanoparticles

Over decades the Ag 3d-level binding energy has been puzzling researchers with its unusual sign and value in silver oxides. For the absolute majority of metals, the metal-to-oxide binding energy shifts are positive and depend significantly on the oxidation state, while in Ag-oxides the oxide shift was time after time reported negative, small, and close for the two very different Ag(I) and Ag(III) oxidation states. In the current work, a photoelectron spectroscopy (PES) investigation on the in -situ created free nanoparticles simultaneously containing both metallic silver and silver-oxide parts provided the grounds to reconsider the old consensus on the Ag-oxide shifts. The Ag 3d energies for the metallic and the oxide parts established in the current experimental work allowed estimating a approximate to 1.2 eV positive shift for the realized oxidation state. This estimate was made possible by using a beam of free nanoparticles with finely controlled composition. The PES experiments on such a beam allowed for a continuous and fast renewal of the poorly conducting sample and for a reliable and accurate calibration relative to vacuum. The constant oxide shift observed at several different oxidation conditions, as well as the relatively narrow and symmetric oxide peaks, point to one dominating oxidation state being present in the particles

Adsorption of polar molecules on krypton clusters

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

Photoelectron spectroscopy of unsupported bismuth clusters: Size related effects of metallic properties

Evolution of metallic properties of free and initially neutral nanoscale Bi clusters has been studied using synchrotron radiation excited photoelectron spectroscopy. The 4f and 5d core as well as the valence levels have been probed. The cross-level analysis indicates metallic properties in Bi clusters in the observed size range from 0.5 nm to 1.4 nm. The behavior of the core-level and valence binding energies as a function of cluster size has been observed to be smooth and relatively consistent. Valence responses for the largest clusters have their shape and width similar to those of the polycrystalline solid Bi. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4759324

Experimental evidence for molecular ultrafast dissociation in O

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

Experimental observation of structural phase transition in CsBr clusters

Formation and growth of CsBr clusters embedded in unsupported Ar clusters was studied using synchrotron radiation photoelectron spectroscopy. The development of the core-level electronic structure for cluster sizes between a few and a few hundred atoms contained information about the local coordination of the constituent particles. The experimental results indicate that a gradual structural phase transition from NaCl structure to CsCl structure for CsBr clusters takes place at around 160 atoms per cluster