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  • Articles: DFG German National Licenses  (59)
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  • Articles: DFG German National Licenses  (59)
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  • 1
    Electronic Resource
    Electronic Resource
    Photochromism of salicylideneaniline (SA). How the photochromic transient is created: A theoretical approach (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 6329-6337 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The theoretical ab initio studies of the singlet states of salicylideneaniline (SA) are presented. The enol, cis-keto and trans-keto tautomers were treated by the HF/6-31G* (geometries and force fields of the ground states), and the CIS (excited states), methods. For the dynamic calculations of the rates of proton transfer (PT) in S1 states, the instanton approach was applied. It was found that the SA molecule in S0 and S1 states of both tautomers needs nonplanarity to stabilize. In the ground state the corresponding angle was calculated as 44° vs the experimental value, 49°. Upon twist of the excited system, the conical intersection of (π,π*) and (n,π*) potential surfaces takes place. In enol form the absolute minimum on the S1 potential energy surface belongs to a strongly twisted (n,π*) state. In keto-form this minimum corresponds to a planar (π,π*) state, while the twisted (n,π*) has the energy (approximate)1055 cm−1 higher. The angles of distortion are equal 93° and 80°, for the enol and keto form, respectively. Both (n,π*) excited tautomers are practically unable to undergo the PT reaction. This, according to the calculations, goes via the planar unstable (π,π*) state. The calculated structures and force-fields lead to the (calculated) proton transfer rate of the order observed experimentally. The calculation of the transfer rate includes multimode nature of the transfer process. The PT cycle of the SA molecule involving the creation of photochromic transient has been proposed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481194
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  • 2
    Electronic Resource
    Electronic Resource
    Quantum-chemical study of the vibronic structure of the phosphorescence and T1→Tn absorption spectra of naphthalene (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 7685-7689 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibronic structure of the phosphorescence spectrum of naphthalene is calculated from ab initio and semiempirical geometries and force-fields of the S0 and T1 states. An excellent agreement with the experiment is obtained. The final triplet state in the triplet→triplet absorption spectrum is identified as 3 3B3g state and the vibronic structure of the 1 3B1u→3 3B3g transition is found in a good agreement with the experimental spectrum. The wavefunction of the 3 3B3g state is dominated by the same electronic configurations as that of the lowest triplet of the same symmetry. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475082
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  • 3
    Electronic Resource
    Electronic Resource
    Rotor-vibrator couplings in partially deuterated toluenes (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 6279-6287 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Fluorescence excitation spectra covering the origin–band region of the two partially methyl-deuterated toluenes (α-deuterotoluene, C6H5CH2D and α-dideuterotoluene, C6H5CHD2) are reported. The spectra, observed in a cold supersonic beam, show transitions between low methyl–rotor levels, and are analyzed in terms of vibrationally adiabatic torsional potentials with two-, four-, and sixfold periodicity. To interpret the resulting potential parameters, ab initio vibrational force field calculations are carried out at the four stationary structures of each isotopomer. The calculations yield accurate values for the adiabatic torsional barriers and qualitatively correct results for the vibrationally adiabatic potentials. Specifically, they show that the twofold potential term dominates in the partially methyl-deuterated isotopomers and that this component has the same magnitude but opposite sign in the mono- and dideuterocompounds. The potential parameters are interpreted in terms of nonbonded interactions between a CH bond of the methyl group and the phenyl ring; specifically, they represent the difference between the interactions of a methyl-CH and a methyl-CD bond with the ortho-CH bonds of the phenyl ring. Modeling of this interaction as a function of H–H separation in terms of a simple analytical expression shows that the repulsive potential is very soft and that individual H–H interactions are of the same order of magnitude as vibrational frequencies. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473618
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  • 4
    Electronic Resource
    Electronic Resource
    Bonding and structure of Y3C2 and Y3C2+ (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 3591-3597 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational frequencies of yttrium normal modes of triyttrium dicarbide neutral and cation have been determined from pulsed field ionization-zero electron kinetic energy photoelectron spectra. The yttrium stretching mode has a frequency of 228 cm−1 in the ion. The two deformation modes have frequencies of 82 and 24 cm−1 in the neutral and a degenerate frequency of 86 cm−1 in the ion. Geometries and ground electronic states have been determined by the comparison of the experiments and theoretical calculations. The cluster has a trigonal bipyramid structure with the ion symmetry of D3h and the neutral C2ν. The ground state is identified as 2B1 for the neutral and 1A1′ for the ion. While the Y–Y bonding has a covalent nature, the Y–C bonding has considerable ionic character. Both the Y–Y and Y–C bonds are stronger in the ion than in the neutral. The enhancement of the Y–Y bonding upon ionization is largely due to the removal of the antibonding 5s character from the yttrium atoms and the Y–C due to the increase of the electrostatic attractions between the yttrium and carbon atoms. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475753
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  • 5
    Electronic Resource
    Electronic Resource
    Mode-specific hydrogen tunneling in tropolone: An instanton approach (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 1203-1212 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Calculations are reported of hydrogen and deuterium tunneling splittings in the ground state S0 (X˜,1A1) and the first excited singlet state S1 (A˜,1B2) of tropolone-d0 and -d1. The main focus of the calculations is on the splittings observed in vibrationally excited levels of S1, some of which are larger while others are smaller than the zero-point splitting. To account for these observations, a potential-energy surface is constructed by standard quantum-chemical methods and the dynamics on this surface is treated by a method derived from the instanton approach. The potential-energy surface is a complete multidimensional surface resulting from the combination of a potential-energy curve along the tunneling coordinate with a harmonic force field calculated at the stationary points. The level of calculation adopted is HF/6-31G** for S0 and CIS/6-31G** for S1. A few other, nominally more accurate, methods were tried but proved to be unsatisfactory. To deal with the dynamics, the instanton method, used previously for the calculation of zero-point level splittings, is modified so as to make it applicable to excited levels. As expected, it is found that excitation of the tunneling mode strongly promotes hydrogen transfer. The effects of exciting modes that are symmetric or antisymmetric with respect to the symmetric transition state are evaluated for all such modes with assigned splittings by a straightforward generalization of the correction terms previously derived for zero-point splittings. Of special interest are out-of-plane modes, some of which show up as overtones with splittings smaller than the zero-point splitting, despite the fact that there is no linear coupling between these modes and the tunneling mode. The effect is ascribed to anharmonic coupling and an effort is made to calculate the required anharmonicities quantum-chemically. In general the agreement between theory and experiment is satisfactory for modes that are linearly coupled while the situation is less clear for anharmonically coupled modes. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470780
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  • 6
    Electronic Resource
    Electronic Resource
    Vibronic structure of the emission spectra from single vibronic levels of the S1 manifold in naphthalene: Theoretical simulation (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 3486-3500 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibrational structure of electronic spectra of naphthalene is simulated by means of a perturbative calculation of the intensities, based on the vibronic basis set. The formalism is implemented to include the contribution of Herzberg–Teller induced activity for totally symmetric modes and to describe the interference between the latter and the allowed Franck–Condon intensity. Geometries, vibrational normal modes, and vibronic coupling parameters required to model the spectra are obtained by means of ab initio and semiempirical calculations. The structure of absorption and single vibronic level fluorescence spectra is reproduced in detail and consistently for all the spectra examined. It is shown that the intensity of modes ν8a and ν5a is strongly affected by interference effects, and that Dushinsky mode mixing of totally symmetric modes plays a major role in redistributing the intensity among the vibronic bands of the spectra. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471054
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  • 7
    Electronic Resource
    Electronic Resource
    The resonance Raman spectrum of cyclobutene (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 5911-5918 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibronic pattern of the resonance Raman spectrum of cyclobutene is simulated by ab initio molecular orbital and by density functional theory calculations. Both Franck–Condon and Herzberg–Teller contributions are included in the analysis of the spectrum. The results suggest an initial dynamics of cyclobutene in the S1 excited state in which the molecule attempts a cis–trans isomerization of the ethylene moiety. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470471
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  • 8
    Electronic Resource
    Electronic Resource
    The structure of Nb3O and Nb3O+ determined by pulsed field ionization–zero electron kinetic energy photoelectron spectroscopy and density functional theory (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 5335-5342 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The geometrical structures of the ground states of triniobium monoxide, Nb3O, and its cation, Nb3O+, have been determined by an experimental and theoretical study. Vibrationally resolved photoelectron spectra of an Nb3O cluster beam were obtained at 100 and 300 K using the pulsed field ionization-zero electron kinetic energy technique. The spectra were simulated by calculating multidimensional Franck–Condon factors using the geometries and harmonic vibrational frequencies obtained from density functional theory for the minimum energy structures of the ion and neutral molecule. The rather remarkable agreement between the experiment and the simulated spectra establishes that Nb3O and Nb3O+ have planar C2v structures with the oxygen atom bridging two niobium atoms. These are the most complex transition metal cluster structures to date to be characterized by gas phase spectroscopic techniques. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470568
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  • 9
    Electronic Resource
    Electronic Resource
    On the vibronic structure of the absorption spectra of radical cations of some polycyclic aromatic hydrocarbons (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 1387-1399 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibronic structure of electronic absorption spectra of four polyacenic radical cations is investigated by means of quantum chemical calculations. We use the semiempirical quantum consistent force field/π electron method (QCFF/PI) augmented by a configuration interaction (CI) scheme that includes all excited configurations having at most one electron in the originally empty molecular orbitals and the ab initio restricted open shell Hartree–Fock (ROHF) method. Displacement parameters for the totally symmetric modes are calculated for different electronic transitions and the resulting Franck–Condon structure is compared with the experimental spectra. The analysis reaffirms the initial interpretation of the absorption spectrum of the cation of naphthalene and reinterprets the recently observed spectrum of the cation of anthracene. First ever analysis of the absorption spectrum of the radical cation of pyrene and perylene is given. For the former, we demonstrate that the unusually large frequency value of the highest ag mode active in the strong absorption band of astronomical interest (443.8 nm) is due to vibronic coupling. For the latter, a resonance vibronic coupling mechanism between manifolds of the 1 2B3g and 1 2B2g states is suggested to explain the doublet structure of the origin of the transition to the latter state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466617
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  • 10
    Electronic Resource
    Electronic Resource
    Phenylynol, PhC.tplbond.COH: First Direct Detection in Solution via Time-Resolved Infrared Spectroscopy (1994)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 116 (1994), S. 6433-6434 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00093a053
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