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The electronic structure of supported mass-selected Ag3 clusters is analyzed by joint femtosecond photoemission spectroscopy and ab initio theoretical investigations. A wide band gap insulating magnesia ultra-thin film on Mo(100) has been chosen as substrate in order to minimize the electronic interaction between metal clusters and support. After magnesia ultra-thin film preparation no photoemission from the molybdenum substrate is observed anymore, instead very weak two photon photoemission is detected possibly originating from surface or subsurface oxide defect states. Soft-landing deposition of 2 ${\%}$ of atomic monolayer equivalents of Ag3 clusters results in the disappearance also of the MgO two photon photoemission signal, while a strong single photon photoemission signal is detected from states located directly below the Fermi level. The theoretical study of structural, electronic and optical properties of Ag3 at two model sites of MgO (100), the stoichiometric MgO(100) and an FS-center defect, based on the DFT method and the embedded cluster model provides insight into the interactions between the cluster and the support which are responsible for the characteristic spectroscopic features. [ABSTRACT FROM AUTHOR]

Density functional calculations have been performed for the V2O5+ reactions towards ethylene considering atomic and molecular oxygen loss, oxygen transfer and association reactions. The oxygen transfer channel to ethylene is energetically favourable in contrast to the oxygen loss. This is in agreement with the experimental results [1] which show that V2O–+ does not lose atomic oxygen during the collision induced dissociation at thermal energies. A radical cation mechanism based on structure-reactivity relation of V2O5+ cluster is proposed to explain oxygen transfer channel indicating that this reaction is size selective. [ABSTRACT FROM AUTHOR]

The ab initio molecular dynamics (AIMD) [1] is combined with the heuristic, successive confinement method of surveying a potential energy surface (PES) [2], thereby offering a framework for the simulation study of kinetics and equilibrium properties of metallic clusters. This approach is applied to the study of Au4, a cluster possessing a simple but specific PES, which consists of very shallow and deep basins and due to this presents a challenge to the conventional AIMD methods. Among other things, the probabilities of the transitions between isomers have been found, and on this basis, both the time-dependent and equilibrium populations of the isomers have been calculated for the conditions typical of the NeNePo experiments [3] in the femtosecond pump-probe spectroscopy. [ABSTRACT FROM AUTHOR]

Ultrafast ground state nuclear dynamics of Au4 and Ag4 is theoretically explored in the framework of negative ion - to neutral - to positive ion (NeNePo) pump-probe spectroscopy based on the ab initio Wigner distribution approach. This involves the preparation of a nonequilibrium neutral ensemble by pump induced photodetachment of a thermal anionic ground state distribution, gradient corrected DFT classical trajectory simulations “on the fly” on the neutral ground state, and detection of the relaxation process of the ensemble in the cationic ground state by a time-delayed probe pulse. In Au4, the initially prepared linear structure is close to a local minimum of the neutral state giving rise to characteristic vibrations in the signals for probe wavelength near the initial Franck-Condon transition. A timescale of ∼1 ps for the structural relaxation towards the stable rhombic D2h neutral isomer was determined by the increase of the signal for probe wavelength in vicinity of the vertical ionization energy of the rhombic structure. In contrast, the relaxation dynamics in Ag4 is characterized by normal mode vibrations since both the initially prepared anionic ground state and the neutral ground state have rhombic minimum geometries. Thus, time-resolved oscillations of pump-probe signals are fingerprints of structural behaviour which can be used experimentally for the identification of particular isomers in the framework of NeNePo spectroscopy. [ABSTRACT FROM AUTHOR]

Density functional calculations using nonlocal functionals for exchange and correlation have been carried out on Ni4 and Ni4(CO) x ( x=1,2) species. In the case of the nonligated cluster, all the forms originated by Jahn–Teller distortion of the tetrahedron have been investigated. The lowest-energy states are all characterized by a spin multiplicity corresponding to the total spin S=2; the four unpaired electrons are strongly localized in the atomic 3 d shells. The Ni–Ni bond is dominated by the s–s interaction, as is proved by changes in electron distribution caused by the ionization. The interaction of the nickel tetramer with one CO ligand has no substantial effect on magnetic properties. On the contrary, two CO groups are already sufficient, when coordinated in a μ2 mode, to quench completely the magnetism of the cluster. The μ2 coordination is found to be more effective in reducing the paramagnetism than the μ3 coordination. [ABSTRACT FROM AUTHOR]

We present the outline of the ab–initio molecular dynamics method for adiabatic excited states which is suitable to treat the involved excited electronic states simultaneously with the motion of the nuclei. The method allows the simulation of time–resolved pump–probe signals and the analysis of the signals in terms of the underlying nuclear dynamics. Moreover, the timescales of the structural relaxation in excited electronic states vs. intramolecular vibrational relaxation processes can be estimated and the influence of the initial temperature of the cluster can be determined. The method is applied to the analysis of the timescales as well as of the dynamics of localized/delocalized electronic excitations in the Na2F molecule which represents a test example for nonstoichiometric alkali–halides with one excess electron. The aim is to develop a method for the investigation of time–dependent laser induced processes in clusters which is capable to extract the leading physical effects responsible for the controlled excitation dynamics and for the evolution of the non–equilibrium states. [ABSTRACT FROM AUTHOR]

We present calculations of absorption patterns in large energy intervals for the stable structures of oxygen-doped- and pure-silver clusters using the linear-response-type approach which allows one to correlate all 11 and 6 electrons per Ag and O atoms, respectively. For this purpose, we designed a new 11-electron relativistic effective core potential (11e–RECP) for Ag atoms at the correlated level of theory, which, together with the associated AO basis set, provide an accurate description of excited states. This has been evidenced by the comparison of our results with available experimental data. We found that inclusion of d electrons in the RECP, as well as in the correlation treatment, is important for an accurate prediction of the complete absorption spectra. Moreover, the influence of d electrons of Ag atoms becomes pronounced, even for structural properties of AgnO clusters. Also, the electrons of oxygen are strongly involved in excitations besides those of Ag-valence electrons, leading to intense transitions spread in a large energy interval. The role O plays in Ag nO clusters differs substantially from the one it plays in oxygen-doped alkali clusters, because of the participation of the d electrons of Ag atoms. [ABSTRACT FROM AUTHOR]

Stable ground state structures for neutral and charged LiH, LiH and NaF ( n↛ m) have been determined using ab - initio methods accounting for electronic correlation effects. The consequences of replacing alkali-atom by foreign-atom or -atoms have been studied. The similarities and differences with respect to topologies of the most stable Li and Na clusters will be pointed out. The ionization potentials and spectroscopic patterns are compared with available experimental data. This allows for the geometrical and spectroscopic assignments as well as for a study of the influence of localized versus non localized bonding on the ground and excited state properties of mixed clusters. [ABSTRACT FROM AUTHOR]

The ground state geometries of small neutral Ag( n=2-9) and charged Ag ( n=2-9) clusters have been determined in the framework of the SCF procedure employing a relativistic pseudopotential accounting for core-valence correlation effects (RECP-CVC). Similarities and differences between neutral and charged clusters have been found. Large scale CI for 5s electrons only has been carried out for determining stabilities, ionization potentials (IP) and vertical detachment energies (VDE) of anions. A comparison between predicted and measured observables allows for the tentative structural assignments. In addition, the low lying energies of excited states for the neutral species at the anionic geometries have been calculated to account fully for geometrical and spectroscopic assignment to the photodetachment measurements. [ABSTRACT FROM AUTHOR]