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  • 11
    Electronic Resource
    Electronic Resource
    Theoretical study of the electronic spectra of cyclopentadiene, pyrrole, and furan (1993)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 115 (1993), S. 6184-6197 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00067a038
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  • 12
    Electronic Resource
    Electronic Resource
    The ab initio calculation of inner sphere reorganization energies of inorganic redox couples (1993)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 115 (1993), S. 2898-2902 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00060a043
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  • 13
    Electronic Resource
    Electronic Resource
    A CI study of the CuCO and CuCO+ complexes (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 1690-1700 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: MO CI calculations are carried out using an optimal space of valence virtual MOs obtained by means of a projection technique, as a linear combination of the AOs which are more occupied in the molecular Fock space. Localization of the occupied MOs and nonvalence virtual MOs is also achieved. The overall procedure is proven to be quite advantageous and well suited to obtain potential energy curves which keep the same physical meaning along the range of distances studied. Using a slightly better than double-zeta quality basis set, a valence CAS-CI, and selected CI wave function by the CIPSI algorithm have revealed a possible weak van der Waals interaction for the 2Σ+ state of CuCO, which remains when polarization functions are added to the basis set for the carbon and oxygen atoms. Even though the CuCO 2Π and CuCO+ 1Σ+ states are energetically close, the nature of the interactions is quite different, π bonding and mainly electrostatic, respectively. The results give further support to the view of the neutral metal–CO interaction as a balance of σ repulsion and π backbonding. However, it is proposed that the driving force for the positive ion metal–CO interaction becomes essentially electrostatic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453234
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  • 14
    Electronic Resource
    Electronic Resource
    Theoretical study of the electronic spectrum of p-benzoquinone (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 9536-9546 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electronic excited states of p-benzoquinone have been studied using multiconfigurational second-order perturbation theory (CASPT2) and extended atomic natural orbital (ANO) basis sets. The calculation of the singlet–singlet and singlet–triplet transition energies comprises 19 valence singlet excited states, 4 valence triplet states, and the singlet 3s,3p, and 3d members of the Rydberg series converging to the first four ionization limits. The computed vertical excitation energies are found to be in agreement with the available experimental data. Conclusive assignments to both valence and Rydberg states have been performed. The main features of the electronic spectrum correspond to the ππ* 1 1Ag→1 1B1u and ππ* 1 1Ag→3 1B1u transitions, computed to be at 5.15 and 7.08 eV, respectively. Assignments of the observed low-energy Rydberg bands have been proposed: An n→3p transition for the sharp absorption located at ca. 7.4 eV and two n→3d and π→3s transitions for the broad band observed at ca. 7.8 eV. The lowest triplet state is computed to be an nπ* 3B1g state, in agreement with the experimental evidence. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478918
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  • 15
    Electronic Resource
    Electronic Resource
    Ab initio study on the low-lying excited states of retinal (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 1112-1122 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio results for the electronic spectrum of all-trans-retinal and its truncated model 3-methyl-all-trans (10-s-cis)-2,4,6,8,10-undecapentaen-1-al are presented. The study includes geometry determination of the ground state. Vertical excitation energies have been computed using multiconfigurational second-order perturbation theory through the CASPT2 formalism. The lowest singlet excited state in gas phase is predicted to be of nπ* character. The lowest triplet state corresponds, however, to a ππ* state. The most intense feature of the spectrum is due to the strongly dipole-allowed ππ* transition, in accordance with the observed maximum in the one-photon spectra. The vertical excitation energies of the Bu- and Ag-like states are found close, the latter (approximate)1 eV higher than the maximum in the two-photon spectra. Solvent effects and nonvertical nature of the observed maximum in the two-photon spectra are invoked in rationalizing the deviation with respect to the best present estimate for the Ag-like state. In addition, qualitative aspects of the one-bond photoisomerization about the C11=C12 double bond of retinal are considered. The overall isomerization picture from 11-cis into all-trans-retinal, as taking place mainly along the triplet manifold, agrees with experimental evidence.© 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473207
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  • 16
    Electronic Resource
    Electronic Resource
    On the theoretical determination of the electron affinity of ozone (1993)
    Springer
    Theoretical chemistry accounts 86 (1993), S. 467-476 
    Details
    ISSN: 1432-2234
    Keywords: Ozone ; Electron affinity ; CAS ; SCF
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Multiconfigurational electron correlation methods have been analyzed in order to theoretically compute the electron affinity (EA) of ozone. The near-degeneracy correlation effects, which are so important in O3 and O 3 − , have been described using complete active space (CAS) SCF wave functions. Remaining dynamic correlation effects are computed using second-order perturbation theory (the CASPT2 method). The best calculated adiabatic value (including zero-point energy corrections), 2.19 eV, is about 0.09 eV larger than the experimental value. Comparative studies using size-consistent coupled pair functional approaches (CPF and ACPF) have also been performed. The harmonic frequencies in O 3 − have been determined to be: ω1=992, ω2=572, and ω3=879 cm−1, which gives a zero-point energy of 0.151 eV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01113945
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  • 17
    Electronic Resource
    Electronic Resource
    The internal rotational barrier of biphenyl studied with multiconfigurational second-order perturbation theory (CASPT2) (1995)
    Springer
    Theoretical chemistry accounts 91 (1995), S. 17-29 
    Details
    ISSN: 1432-2234
    Keywords: Biphenyl ; Rotational barrier ; Perturbation theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A detailedab initio study of the molecular structure and rotational barriers of biphenyl has been performed. First, non-dynamical correlation effects involving the π system are taken into account at the CASSCF level. These wave functions are subsequently employed as reference functions in a multiconfigurational second-order perturbation treatment (CASPT2). The performance single-reference approaches is in addition analysed. The molecular geometries of biphenyl in twisted, coplanar, and perpendicular conformations have been optimized at the CASSCF level. A rotational angle of 44.3° is predicted for the minimum energy conformer in agreement with gas-phase electron diffraction data (44.4±1.2°). The highest level of theory employed yields the values 12.93 (6.0±2.1) and 6.40 (6.5±2.5) kJ/mol for the barrier heights at 0° and 90°, respectively (electron diffraction data within parentheses). In the light of the present findings, the reliability of the available experimental data is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01113859
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  • 18
    Electronic Resource
    Electronic Resource
    Density matrix averaged atomic natural orbital (ANO) basis sets for correlated molecular wave functions (1995)
    Springer
    Theoretical chemistry accounts 92 (1995), S. 149-181 
    Details
    ISSN: 1432-2234
    Keywords: Basis sets ; Atomic natural orbitals ; General contraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Generally contracted basis sets for the first row transition metal atoms Sc-Zn have been constructed using the atomic natural orbital (ANO) approach, with modifications for allowing symmetry breaking and state averaging. The ANOs are constructed by averaging over the three electronic configurationsd n ,d n−1 s, andd n−2 s 2 for the neutral atom as well as the ground state for the cation and the ground state atom in an external electric field. The primitive sets are 21s15p10d6f4g. Contraction to 6s5p4d3f2g yields results that are virtually identical to those obtained with the corresponding uncontracted basis sets for the atomic properties, which they have been designed to reproduce. Slightly larger deviations are obtained with the 5s4p3d2f1g for the polarizability, while energetic properties still have only small errors. The design objective has been to describe the ionization potential, the polarizability and the valence spectrum as accurately as possible. The result is a set of well-balanced basis sets for molecular calculations, which can be used together with basis sets of the same quality for the first and second row atoms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01114922
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  • 19
    Electronic Resource
    Electronic Resource
    A theoretical determination of the electronic spectrum of formaldehyde (1995)
    Springer
    Theoretical chemistry accounts 92 (1995), S. 227-239 
    Details
    ISSN: 1432-2234
    Keywords: Formaldehyde ; Electronic spectrum ; Perturbation theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The electronically excited states of formaldehyde are examined by means of multiconfigurational second-order perturbation (CASPT2) theory with extended ANO-type basis sets. The calculations comprised five valence excited states plus all singlet 3s, 3p, and 3d members of the Rydberg series converging on the first ionization. The computed vertical excitation energies were found to be within 0.2 eV of the available experimental energies. Full geometry optimization has been performed for five valence excited states. Assuming a planar geometry, the “0-0” transition for the valence1A1(π → π*) state is calculated to appear near 7.9 eV, close to the (n y → 3p) region. This state is, however, not planar and the true adiabatic energy is 7.4 eV, which is 2.3 eV below the corresponding vertical transition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01125948
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  • 20
    Electronic Resource
    Electronic Resource
    A restricted active space (RAS) SCF study of the lifetime of theA 3Π state of OH+ (1991)
    Springer
    Theoretical chemistry accounts 79 (1991), S. 81-92 
    Details
    ISSN: 1432-2234
    Keywords: Hydroxyl ionA 3Π state ; Restricted active space (RAS) SCF ; Active orbitals ; Bond distances
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Restricted Active Space (RAS) SCF calculations have been performed of the potential curves for theX 3Σ− andA 3Π states of the OH+ ion and on the lifetime of thev=0−2 vibrational levels of theA state. The convergence of the transition moment integral as a function of the size of the active orbital space was used to select the active orbitals. The calculated value of thev=0 lifetime is 2.4 µs. An estimate of the errors remaining in the calculation leads to a final theoretical value of 2.7±0.1 µs. Computed bond distances and bond energies are 1.031 (1.029) Å and 5.05 (5.01) eV, respectively, for theX state, and 1.137 (1.135) Å and 1.57 eV, respectively, for theA state (experimental values within parenthesis).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01127097
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