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  • AIP Publishing  (6)
  • 2000-2004  (6)
  • 1
    Online Resource
    Online Resource
    Electronic excited states of conjugated cyclic ketones and thioketones: A theoretical study
    AIP Publishing ; 2002
    In:  The Journal of Chemical Physics Vol. 117, No. 4 ( 2002-07-22), p. 1649-1659
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 117, No. 4 ( 2002-07-22), p. 1649-1659
    Abstract: Absorption spectra of a series of cyclic conjugated ketones and thioketones have been computed at the multiconfigurational second-order multistate perturbation level of theory, the CASSCF/MS-CASPT2 method. Excitation energies, transition dipole moments, oscillator strengths, and static dipole moments are reported and discussed for excited states with energies lower than ≈7–8 eV. The main bands of the spectra have been assigned and characterized in most cases for the first time. The spectroscopy of the different systems is compared in detail. Thioketones in particular have low-energy and intense ππ* transitions which suggest corresponding enhanced nonlinear molecular optical properties. Additionally, some of the methods used to estimate these properties from spectroscopic data have been considered in order to analyze the main contributions to the nonlinear optical properties.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1482706
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2002
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 2
    Online Resource
    Online Resource
    Static electric properties of conjugated cyclic ketones and thioketones
    AIP Publishing ; 2000
    In:  The Journal of Chemical Physics Vol. 113, No. 15 ( 2000-10-15), p. 6235-6244
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 113, No. 15 ( 2000-10-15), p. 6235-6244
    Abstract: The results of ab initio calculations of static electric properties of a series of cyclic conjugated ketones and thioketones are presented. Dipole moments, dipole polarizabilities, as well as the first and second hyperpolarizabilities, were evaluated at different levels of theory: SCF, CASSCF, MP2, CCSD, CCSD(T), and CASPT2 methods were used. Both MP2 and CASPT2 methods have been shown to perform well in the calculation of such properties. The dependence of the electric properties on the extent of the π-electron conjugation and on the replacement of the keto by the thioketo group is analyzed. Cyclic conjugated thioketones are shown to exhibit significant nonlinear electric properties which make them prospective building blocks for nonlinear optical materials.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1290012
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2000
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 3
    Online Resource
    Online Resource
    A theoretical study of the 1B2u and 1B1u vibronic bands in benzene
    AIP Publishing ; 2000
    In:  The Journal of Chemical Physics Vol. 112, No. 6 ( 2000-02-08), p. 2798-2809
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 112, No. 6 ( 2000-02-08), p. 2798-2809
    Abstract: The two lowest bands, 1B2u and 1B1u, of the electronic spectrum of the benzene molecule have been studied theoretically using a new method to compute vibronic excitation energies and intensities. The complete active space (CAS) self-contained field (SCF) method (with six active π-orbitals) was used to compute harmonic force field for the ground state and the 1B2u and 1B1u electronic states. A linear approximation has been used for the transition dipole as a function of the nuclear displacement coordinates. Derivatives of the transition dipole were computed using a variant of the CASSCF state interaction method. Multiconfigurational second-order perturbation theory (CASPT2) was used to obtain absolute excitation energies (12 active π-orbitals). The results show that the approach works well. Vibrational progressions are well described in both bands and intensities, and energies are in agreement with experiment, in particular when CASPT2 derived geometries are used. One interesting result is that computed vertical energies fall about 0.1 eV on the high energy side of the band maximum.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.480854
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2000
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 4
    Online Resource
    Online Resource
    Theoretical characterization of the lowest-energy absorption band of pyrrole
    AIP Publishing ; 2002
    In:  The Journal of Chemical Physics Vol. 116, No. 17 ( 2002-05-01), p. 7526-7536
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 116, No. 17 ( 2002-05-01), p. 7526-7536
    Abstract: The lowest-energy band of the electronic spectrum of pyrrole has been studied with vibrational resolution by using multiconfigurational second-order perturbation theory (CASPT2) and its multistate extension (MS–CASPT2) in conjunction with large atomic natural orbital-type basis sets including Rydberg functions. The obtained results provide a consistent picture of the recorded spectrum in the energy region 5.5–6.5 eV and confirm that the bulk of the intensity of the band arises from a ππ* intravalence transition, in contradiction to recent theoretical claims. Computed band origins for the 3s,3p Rydberg electronic transitions are in agreement with the available experimental data, although new assignments are suggested. As illustrated in the paper, the proper treatment of the valence–Rydberg mixing is particularly challenging for ab initio methodologies and can be seen as the main source of deviation among the recent theoretical results as regards the position of the low-lying valence excited states of pyrrole.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1465406
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2002
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 5
    Online Resource
    Online Resource
    Multiconfigurational second-order perturbation study of the decomposition of the radical anion of nitromethane
    AIP Publishing ; 2004
    In:  The Journal of Chemical Physics Vol. 121, No. 9 ( 2004-09-01), p. 4127-4132
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 121, No. 9 ( 2004-09-01), p. 4127-4132
    Abstract: The doublet potential energy surfaces involved in the decomposition of the nitromethane radical anion (CH3NO2−) have been studied by using the multistate extension of the multiconfigurational second-order perturbation method (MS-CASPT2) in conjunction with large atomic natural orbital-type basis sets. A very low energy barrier is found for the decomposition reaction: CH3NO2−→[CH3NO2]−→CH3+NO2−. No evidence has been obtained on the existence of an isomerization channel leading to the initial formation of the methylnitrite anion (CH3ONO−) which, in a subsequent reaction, would yield nitric oxide (NO). In contrast, it is suggested that NO is formed through the bimolecular reaction: CH3+NO2−→[CH3O-N-O] −→CH3O−+NO. In particular, the CASSCF/MS-CASPT2 results indicate that the methylnitrite radical anion CH3ONO− does not represent a minimum energy structure, as concluded by using density functional theory (DFT) methodologies. The inverse symmetry breaking effect present in DFT is demonstrated to be responsible for such erroneous prediction.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1772357
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2004
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 6
    Online Resource
    Online Resource
    The electronic spectra of aryl olefins: A theoretical study of phenylacetylene
    AIP Publishing ; 2003
    In:  The Journal of Chemical Physics Vol. 119, No. 8 ( 2003-08-22), p. 4294-4304
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 119, No. 8 ( 2003-08-22), p. 4294-4304
    Abstract: The electronic absorption and emission spectra of phenylacetylene have been studied by means of a multiconfigurational second-order perturbation method and its multistate extension. The low-lying valence singlet and triplet π→π* excited states together with 3s3p3d members of the two lowest Rydberg series have been computed in the vertical spectrum. By optimization of the geometries of the ground and low-lying excited states and the calculation of transition energies and properties, the obtained results lead to a detailed analysis and assignment of the available experimental absorption spectrum and to the description of the basic features of the emission processes in phenylacetylene. Vibrational frequencies for the two lowest singlet and triplet excited states have also been computed. The spectroscopy of phenylacetylene is finally related to that of other aryl olefins such as styrene and benzaldehyde. Differences and similarities of their excited state structures are discussed.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1594175
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2003
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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