The Experts below are selected from a list of 213 Experts worldwide ranked by ideXlab platform
Mark B Knickelbein - One of the best experts on this subject based on the ideXlab platform.
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photoIonization spectroscopy of yttrium clusters Ionization Potentials for yn and yno n 2 31
Journal of Chemical Physics, 1995Co-Authors: Mark B KnickelbeinAbstract:The photoIonization spectra of yttrium clusters Yn, and their monoxides YnO have been recorded for n=2–31. As has been observed for other transition metal clusters, the vertical Ionization Potentials decrease rapidly yet nonmonotonically to ∼10 atoms, beyond which a more gradual decrease takes place. The Ionization Potentials of the cluster monoxides were found to be similar to those of the corresponding bare clusters except for n≤10 where differences of 0.1–0.3 eV were observed in some cases. The absence of magic numbers or odd–even alternations is taken as evidence that threshold photoIonization occurs from a localized 4d orbital rather than a delocalized band derived from 5s valence electrons.
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electronic shell structure in the Ionization Potentials of copper clusters
Chemical Physics Letters, 1992Co-Authors: Mark B KnickelbeinAbstract:Abstract The Ionization Potentials (IPs) of copper clusters (Cu n ) up to 150 atoms have been bracketed using laser photoIonization. Large decreases in IP at n = 2, 8, 20, 30, 34, 40 and 60 atoms are observed, as well as a strong odd—even alternation extending beyond 100 atoms. These features correspond to electronic shell and subshell closings predicted for systems of n valence electrons confined to spherical or spheroidal Potentials. The decreases in IP expected to accompany shell closings at n = 58 and 92 are absent, however, and a new set of local extrema are observed, including local maxima at n = 57 and 88–91 and minima at n = 49 and 92. The possibility of perturbations to the electronic energy level structure due to geometric packing constraints is discussed.
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photoIonization studies of transition metal clusters Ionization Potentials for fen and con
Journal of Chemical Physics, 1990Co-Authors: Shihe Yang, Mark B KnickelbeinAbstract:The photoIonization efficiency (PIE) spectra for cold iron clusters (Fe6–Fe90) and cobalt clusters (Co3, Co7–Co92) have been measured using a tunable ultraviolet laser combined with time‐of‐flight mass spectrometry. Vertical Ionization Potentials (IPs) assigned from the observed photoIonization thresholds decrease rapidly but nonmonotonically for both Fen and Con up to n≅20, beyond which IPs evolve more slowly and smoothly. The measured IPs for both iron and cobalt clusters are lower than those predicted by the conducting spherical droplet model. The evolution of IP with increasing cluster radius R is observed to occur more gradually than the R−1dependence predicted by this model. This suggests that the Fermi energy for clusters in this size range decreases with increasing cluster size. The shapes of the PIE spectra near threshold are observed to continuously evolve with increasing cluster size, with the smallest clusters displaying photoIonization efficiencies which rapidly increase with energy above thr...
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near threshold photoIonization of nickel clusters Ionization Potentials for ni3 to ni90
Journal of Chemical Physics, 1990Co-Authors: Mark B Knickelbein, Shihe Yang, S J RileyAbstract:The threshold photoIonization efficiency (PIE) curves for nickel clusters in the size range Ni3 to Ni90 have been measured by laser photoIonization with detection by time‐of‐flight mass spectrometry. Both warm (≤298 K) and cold (≤77 K) clusters have been studied. The PIE curves for 298 K clusters display thermal tails, while these tails are smaller for cold clusters. Cluster Ionization Potentials (I.P.s) have been determined by two methods: the Watanabe procedure and linear extrapolation of the PIE curves. Dramatic dependence of I.P. on cluster size is found for clusters smaller than 11 atoms, while the I.P.s of larger clusters decrease relatively smoothly and nearly monotonically from 5.84 eV for Ni11 to 5.56 eV for Ni90. The I.P.s for clusters larger than Ni40 show the linear dependence on reciprocal radius (R−1) predicted by the conducting spherical drop model of small particle I.P.s, but do not fit the model quantitatively unless the limiting (R−1→ 0) work function is reduced by 0.46 eV from the bulk ...
Daniel Rocasanjuan - One of the best experts on this subject based on the ideXlab platform.
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ab initio determination of the Ionization Potentials of water clusters h2o n n 2 6
Journal of Chemical Physics, 2012Co-Authors: Javier Segarramarti, Manuela Merchan, Daniel RocasanjuanAbstract:High-level quantum-chemical ab initio coupled-cluster and multiconfigurational perturbation methods have been used to compute the vertical and adiabatic Ionization Potentials of several water clusters: dimer, trimer, tetramer, pentamer, hexamer book, hexamer ring, hexamer cage, and hexamer prism. The present results establish reference values at a level not reported before for these systems, calibrating different computational strategies and helping to discard less reliable theoretical and experimental data. The systematic study with the increasing size of the water cluster allows obtaining some clues on the structure and reductive properties of liquid water.
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ab initio determination of the Ionization Potentials of dna and rna nucleobases
Journal of Chemical Physics, 2006Co-Authors: Daniel Rocasanjuan, Mercedes Rubio, Manuela Merchan, Luis SerranoandresAbstract:Quantum chemical high level ab initio coupled-cluster and multiconfigurational perturbation methods have been used to compute vertical and adiabatic Ionization Potentials of the five canonical DNA and RNA nucleobases: uracil, thymine, cytosine, adenine, and guanine. Several states of their cations have been also calculated. The present results represent a systematic compendium of these magnitudes, establishing theoretical reference values at a level not reported before, calibrating computational strategies, and guiding the assignment of the features in the experimental photoelectron spectra.
Jerzy Leszczynski - One of the best experts on this subject based on the ideXlab platform.
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relativistic two component infinite order method for atomic core Ionization Potentials
Journal of Chemical Physics, 2007Co-Authors: Maria Barysz, Jerzy LeszczynskiAbstract:In this paper the authors have applied the infinite-order two-component method (IOTC) to compute the valence and inner shell Ionization Potentials for the Ne, Ar, Kr, and Xe elements. The obtained results show the very good performance of the recently defined relativistic IOTC method. They also confirm the importance of the relativistic effects in the determination of the inner shell Ionization Potentials.
Henry F Schaefer - One of the best experts on this subject based on the ideXlab platform.
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Ionization Potentials of small lithium clusters lin and hydrogenated lithium clusters linh
Journal of Chemical Physics, 2005Co-Authors: Steven E Wheeler, Henry F SchaeferAbstract:We present accurate Ionization Potentials (IPs) for small lithium clusters and hydrogenated lithium clusters (n=1–4), computed using coupled-cluster singles and doubles theory augmented with a perturbative correction for connected triple excitations [CCSD(T)] with the correlation-consistent weighted core-valence quadruple-ζ basis set (cc-pwCVQZ). In some cases the full CCSDT method has been used. Comparison of computed binding energies with experiment for the pure cationic lithium clusters reveals excellent agreement, demonstrating that previous discrepancies between computed and experimentally derived atomization energies for the corresponding neutral clusters are due to the use of an inaccurate experimental IP for Li4. The experimental IP for Li4 falls 0.43eV below our theoretical adiabatic value of 4.74eV, which should be a lower bound to the measured IP. Our recommended zero-point corrected adiabatic IPs for Li, Li2, Li3, Li4, LiH, Li2H, Li3H, and Li4H are 5.39, 5.14, 4.11, 4.74, 7.69, 3.98, 4.69, and...
L S Cederbaum - One of the best experts on this subject based on the ideXlab platform.
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inner shell single and double Ionization Potentials of aminophenol isomers
Journal of Chemical Physics, 2011Co-Authors: Nikolai V Kryzhevoi, Robin Santra, L S CederbaumAbstract:A comprehensive study of single and double core Ionization Potentials of the aminophenol molecule is reported. The role of relaxation, correlation, relativistic, and basis set effects in these Potentials is clarified. Special attention is paid to the isomer dependence of the single and double core Ionization Potentials. Some of them are also compared with the respective values of the phenol and aniline molecules. It is shown that the core level single Ionization Potentials of the para-, meta-, and ortho-aminophenol molecules differ only slightly from each other, rendering these structural isomers challenging to distinguish for conventional x-ray photoelectron spectroscopy. In contrast, the energy needed to remove two core electrons from different atoms depends noticeably on the mutual arrangement and even on the relative orientations of the hydroxyl and amine groups. Together with the electrostatic repulsion between the two core holes, relaxation effects accompanying double core Ionization play a crucial role here. The pronounced sensitivity of the double Ionization Potentials, therefore, enables a spectroscopic characterization of the electronic structure of aminophenol isomers by means of x-ray two-photon photoelectron spectroscopy.
