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  • 1
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 7884-7892 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A one-electron pseudopotential model is used to calculate the excited states of NanFn−1 clusters in the range 2≤n≤29. The transition dipole moments are derived to determine the vertical absorption lines from the ground state. Monte Carlo simulations based on the Franck–Condon principle are also achieved to obtain finite temperature absorption spectra. The analysis of ground and excited orbitals in various situations illustrates the rather simple nature of the excitations which are interpreted through an analogy with s−p type transitions in atoms. The influence of electron localization in the initial state is pointed out. Comparison of the simulated spectra with experimental data provides additional keys to understand and discuss the relationship between structure, electron localization, and spectroscopic properties. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 7871-7883 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We introduce a one-electron pseudopotential model to study the structural and electronic properties of excess-electron alkali halide clusters. This model assumes total charge transfer between alkali and halide atoms. This ionic part of the system is described via repulsive and Coulomb potentials. The remaining electrons of the excess metal atoms are treated within an explicit quantal scheme via ion–electron pseudopotentials. Moreover, explicit core-polarization and core-electron correlation contributions are taken into account. This model is used to derive ground state structural, energetics, and electronic properties of one-excess electron NanFn−1 clusters in the range 2≤n≤29. We show that the structural characters are closely related with electron localization and we propose a classification into five types, two of them exhibiting rather strong localization namely F-centers and Na-tail structures, the others exhibiting a less bound electron localizing in a surface-state, an edge-state, or on an atom-depleted face of the cluster. Although we observe an energetical predominance of cubiclike structures, hexagonal isomers are seen to appear as stable ones and exhibit similar localization features. The various energy contributions to the stability are examined. All studied NanFn−1 clusters are found stable with respect to fragmentation. The ionization potentials, which are seen to reflect faithfully the localization character, are discussed in details and compared with consistent recent experimental data. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 4148-4158 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We present a calculation of the structure and the optical transitions of sodium atoms and dimers embedded in argon clusters and matrices. We studied several different systems: A single sodium atom in a dodecahedral argon cluster, a Na atom in a substitutional site of a fcc (face-centered-cubic) Ar lattice containing 63 atoms and a sodium dimer in a 9-atom vacancy of the same fcc lattice (Na2@Ar54). For optimizing the system geometry in its ground state, we use a simplified tight-binding scheme of a metal cluster dressed by the metal-matrix and matrix-matrix van der Waals interactions. A procedure closer to ab initio methodology is then applied using e-Na+ and e-Ar semi-local pseudopotentials and core-polarization operators to determine the electronic structure of the metal valence electrons in the environment of the rare-gas atoms. The electronic transitions and oscillator strengths are obtained by a full two-electron configuration interaction (CI) treatment in the case of Na2@Ar54. The A1Σu+→X1Σg+ transition is redshifted in comparison to the free Na2 dimer. This phenomenon does not appear in the case of a matrix-isolated atom, where all lines are blueshifted. © 1998 American Institute of Physics.
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  • 4
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 9021-9026 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The temperature dependence of the emissions from the 0+(3P1)and 1(3P2) Kr*Ar exciplex states in the range 85–350 K was studied using time resolved techniques, vacuum ultraviolet synchrotron radiation, and argon samples doped with minimal amounts of krypton. As the temperature is increased, the emission shifts to the blue, its width increases by almost a factor of 2, and the line shape becomes asymmetrical. The experimental line shapes have been simulated by means of Franck–Condon density calculations using the available ground state potential of Aziz and Slaman [Mol. Phys. 58, 679 (1986)] and by modeling the exciplex potentials as Morse curves. The potential parameters for the 0+ and 1 states are re=5.05±0.01 and 5.07±0.01 a0, respectively; De=1150±200 cm−1 and β=1.4±0.1 a0−1 for both states. The latter two values yield ωe=140 cm−1 and ωexe=4.3 cm−1. The energy positions of the exciplexes's wells and their depths are compared with published results. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 6426-6438 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The electronic structure of IF is investigated using ab initio pseudopotentials and a variational/perturbative MRCI scheme (CIPSI/CIPSO). All the valence states dissociating into neutral asymptotes I(2P1/2,2P3/2)+F(2P1/2,2P3/2) and ionic asymptotes I+(3P2,3P1,3P0,1D2,1S0) +F−(1S0) are determined up to the region where they undergo avoided crossing with the neutral excited states dissociating into I*+F. The spectroscopic properties are derived and discussed in comparison with the available experimental results, with emphasis on the X, B, E, A, β, A′, and D′ states. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 1492-1499 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A pseudopotential hole-particle formalism is developed for the treatment of rare-gas excimers and excited rare-gas clusters. The formalism relies on the definition of a model Hamiltonian on the basis of single hole-particle excitations (from the neutral closed shell ground state) involving localized np hole orbitals and any orthogonal molecular orbital (MO) basis set for the excited particle. Hole contributions in the Hamiltonian matrix elements are taken into account via distance- and orientation-dependent transfer integrals (hole delocalization) and repulsion integrals like in diatomic in molecules treatments of rare gas ions, while the contribution of the excited particle is included through an explicit quantal treatment via one-electron e-Rg and averaged e-Rg+ pseudopotentials. Core-polarization pseudopotentials are also added to account for core-polarization and core-Rydberg correlation effects. Some approximated core-Rydberg two-electron integrals needed for adequate space and spin multiplicity of the excited states are also included. The possible applications and extensions of this formalism are discussed. © 1996 American Institute of Physics.
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  • 7
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 1500-1515 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A pseudopotential hole-particle model (corresponding to the formalism introduced in paper I) is applied to the determination of the Rydberg states of the Ar2* excimer with and without spin–orbit coupling. All the Λ–Σ Rydberg states (without spin–orbit coupling) adiabatically dissociating into Ar+Ar* (4s,4p,3d,5s,5p,4d), are investigated and all Ω states adiabatically dissociating into Ar+Ar*(4s,4p) have been determined including spin–orbit coupling. The calculation also includes at short distance attractive molecular configurations diabatically correlated with higher atomic asymptotes. The nature of the Λ–Σ states is analyzed and assigned with reference to the Rydberg orbitals of the Kr* united atom limit. Extensive comparison with previous calculations and experiments is carried on. For the lowest ungerade states (1)1u, 0−u, (1)0+u, and (2)0+u, good quantitative agreement is found with experimental high resolution studies. Several members of Rydberg series are calculated and assigned, yielding intra-Rydberg transition energies (1)3Σ+u((1)1u,0−u)→m 3Πg or m 3Σ+g in good correspondence with recent intra-Rydberg spectroscopy experiments. In particular the present calculation provides a likely interpretation of the infrared spectra of Ar2* as due to (1)3Σ+u→(1)3Σ+g transitions with an upper corresponding Ω state (1)1g,0−g containing quasi-bound vibrational levels. © 1996 American Institute of Physics.
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  • 8
    Digitale Medien
    Digitale Medien
    Springer
    The European physical journal 4 (1998), S. 219-224 
    ISSN: 1434-6079
    Schlagwort(e): PACS. 31.50.+w Excited states[:AND:] 31.70.Dk Environmental and solvent effects
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract: We present a pseudopotential method to study the absorption spectroscopy of NO in an argon matrix modeled by a large albeit finite cluster. The excited states of NO are described with the virtual orbitals of a NO+ Hartree-Fock calculation plus a core-polarization operator to account for the electron-NO+ correlation. The argon atoms of the matrix are replaced by pseudopotentials for the repulsive contributions and core-polarization operators to account for matrix polarization and correlation with the excited electron. The model is shown to account for the matrix-induced transition shifts and also for the cut-off of the Rydberg series for n 〉3 reported in absorption experiments from the ground state.
    Materialart: Digitale Medien
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  • 9
    ISSN: 1434-6079
    Schlagwort(e): PACS. 36.40.-c Atomic and molecular clusters - 36.40.Mr Spectroscopy and geometrical structure of clusters
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract: The geometrical structure of ground state Ban clusters (n =2-14) has been predicted from various types of calculations including two ab initio approaches used for the smaller sizes namely HF+MP2( n =2-6), DFT (LSDA)( n =2-6, 9) and one model approach HF+pairwise dispersion used for all sizes investigated here. The lowest energy configurations as well as some isomers have been investigated. The sizes n =4, 7 and 13 are predicted to be the relatively more stable ones and they correspond to the three compact structures: the tetrahedron, the pentagonal bipyramid and the icosahedron. The growth behavior from Ba7 to Ba13 appears to be characterized by the addition of atoms around a pentagonal bipyramid leading to the icosahedral structure of Ba13 which is consistent with the observed size-distribution of barium clusters. Values for vertical ionization potentials calculated for n =2-5 at the CI level are seen to be in quite good agreement with recent measures.
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