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  • 1
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 345-356 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The nuclear dynamics on potential energy surfaces with a conical intersection is investigated on the basis of exact (numerical) integration of the time-dependent Schrödinger equation. The ethylene cation is chosen as a typical realistic model system. Complementing earlier work we study the dynamics also in the adiabatic basis, which will be seen to allow for a more profound understanding of the decay and dephasing processes occurring in the system. The computational effort exceeds considerably that of propagation in the diabatic basis, to which previous related studies have been confined. To solve the resulting computational problems we develop and present a special multidimensional adaptation of the finite basis set method utilizing the product structure of the basis. It allows us to calculate propagation in a general potential including three vibrational modes. For the time integration a fourth order differencing scheme is introduced which is faster than the second order differencing-scheme and predictor–corrector approaches.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 5166-5166 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 1045-1061 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The intramolecular non–Born–Oppenheimer quantum dynamics on conically intersecting potential-energy surfaces is analyzed on the basis of exact (numerical) time-dependent quantum calculations for two representative two-state three-mode vibronic-coupling models. A compact description of the time-dependent dynamics in terms of reduced density matrices of the electronic and vibrational subsystems is introduced. Results are presented for the time evolution of electronic and vibrational coherences, populations, as well as subsystem entropies. It is found that such simple two-state three-mode vibronic coupling models exhibit a rich variety of dissipative phenomena on femtosecond time scales. The numerical results reveal an interesting interplay of driven electronic surface-hopping processes and dephasing of coherent vibrational motion which is presumably a generic feature of ultrafast internal conversion processes in polyatomic molecules.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 3934-3947 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We introduce a general Hamiltonian describing two coupled subsystems, each having a finite zero-order decay probability. With use of simple statistical assumptions on the underlying states, we derive new probability distributions of individual decay rates. We analyze the cases of weak and intermediate to strong coupling, respectively. The resulting distributions often resemble a suitable χ2 distribution, but do not belong to that class of functions. An interpretation of decay rates in terms of a χ2 model thus may lead to wrong conclusions. As a concrete realization, we study a Hamiltonian describing the non-Born–Oppenheimer coupling of two electronic states via the nuclear motion. The model is applied to the calculation of absorption-type spectra of NO2 and C2H+4. We investigate statistical properties of energy levels, line intensities, and decay rates. For NO2, we find from all statistics a completely irregular behavior, consistent with random matrix predictions and demonstrating the strong mixing of zero-order states due to the nonadiabatic coupling. For C2H+4, all statistics exhibit characteristic deviations from the irregular limit that can be given a consistent interpretation.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 2023-2040 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The static and dynamic aspects of the vibronic interaction of the B˜ 2E2g and C˜ 2A2u electronic states of C6H+6 are analyzed. In the approximation of linear vibrational and vibronic coupling, the model Hamiltonian for this system comprises eight nonseparable vibrational modes, six of which are degenerate (two of A1g symmetry, four of E2g symmetry, and two of E2u symmetry). The coupling constants are estimated from existing ab initio SCF and semiempirical (CNDO/S) calculations. The topology of the adiabatic potential-energy surfaces of this class of model Hamiltonians is investigated. It is shown that the model exhibits a variety of conical intersections which dominate the vibronic dynamics. The dynamical problem is solved with simultanteous inclusion of six vibrational modes, four of which are degenerate (the Jahn–Teller coupling of two of the E2g modes is negligible). Hamiltonian matrices with dimensions up to 6×106 are diagonalized using the Lanczos algorithm. After some adjustments of coupling constants, the calculation reproduces well the complex structure of the overlapping B˜ 2E2g–C˜ 2A2u bands in the photoelectron spectrum of benzene. The vibronic structure of the lower-energy E2g band is dominated by a two-mode Jahn–Teller effect in the B˜ state. At higher energy, the marked diffuseness of the "C˜ 2A2u band'' is shown to be a consequence of complete vibronic mixing with the lower-lying B˜ state. Based on thenumerical solution of the full problem, the reliability of approximations (neglect of nonseparability of modes, introduction of a single effective pseudo-Jahn–Teller mode) is assessed. A time-dependent analysis reveals an ultrafast decay of the population of the C˜ state on a time scale of about 20 fs, followed by quasiperiodic recurrences which are damped on a time scale of a few hundred femtoseconds. These findings underline the importance of conical intersections and strong nonadiabatic effects also for larger molecules such as aromatic hydrocarbons. They demonstrate that nowadays a full quantum treatment is feasible also for these larger systems.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 117 (2002), S. 2657-2671 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The multistate vibronic dynamics in the X˜ 2E1g-E˜ 2B2u electronic states of the benzene radical cation is investigated theoretically by an ab initio quantum-dynamical approach. The vibronic coupling scheme and the ab initio values of the system parameters are adopted from the previous Paper I. Vibronic line spectra are obtained with the Lanczos procedure. Extensive calculations on wave-packet propagation have been performed with the aid of the multiconfiguration time-dependent Hartree method. Up to five coupled electronic potential energy surfaces and 13 vibrational degrees of freedom have been included in these calculations. As a result, the impact of a third electronic state (X˜ or B˜) on a strongly coupled manifold (B˜-C˜ or D˜-E˜ states) is quantitatively assessed. It leads to a restructuring of the spectral envelope which is stronger for the B˜-D˜-E˜ than for the X˜-B˜-C˜ system. The internal conversion dynamics is characterized by a stepwise transfer of electronic population to the lowest electronic state on a time scale of ∼100 fs, if the system is prepared initially on the highest potential energy surface. Companion calculations have also been performed for the case when the system is prepared in the intermediate state at t=0; they show a branching of the electronic populations. These are all novel findings which are discussed in terms of a series of conical intersections between the various potential energy surfaces. The importance of such multistate vibronic interactions for the photophysics and photochemistry of medium-sized systems is pointed out. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The valence photoelectron spectrum of allene (C3H4) pertinent to the A˜ 2E/B˜ 2B2 interacting electronic manifold of the corresponding cation (C3H4+) is theoretically calculated and compared with the most recent high resolution He I excited experimental recording of Baltzer et al.[Chem. Phys. 196, 551 (1995)]. A model diabatic Hamiltonian within the linear vibronic coupling scheme and ab initio calculated coupling parameters are employed in our investigations. While the resolved vibrational progressions in the photoelectron band at low energies can be attributed to the E⊗B Jahn–Teller activity within the A˜ 2E electronic manifold, the diffuse structure in the photoelectron band at high energies is found to emerge from the mixing of the A˜ 2E electronic manifold with the B˜2B2 electronic state via degenerate vibrational modes. The latter demonstrates the importance of the pseudo-Jahn–Teller type of interactions in the photoelectron spectrum of allene. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Negative ion photoelectron spectra of NO2− at 266 nm (4.660 eV) and 351 nm (3.532 eV) are theoretically calculated and compared with earlier experimental findings. A diabatic model Hamiltonian with linear vibronic coupling between the conically intersecting X˜ 2A1 and A˜ 2B2 states of NO2 is employed for this purpose. While the linear vibronic coupling model successfully reproduces the low resolution experimental photoelectron spectrum at 266 nm, second order coupling terms are necessary for the high resolution spectrum at 351 nm. The vibronic structure of the X˜ 2A1 state of NO2 in the photoelectron spectrum is found to be almost unaffected by the nonadiabatic coupling, whereas, the latter has a strong impact on the vibronic structure of the A˜ 2 B2 state. The magnitude of the vibronic coupling constant, which has otherwise been overestimated by earlier theoretical studies, is calculated ab initio and its limits of validity are confirmed by the results from different ab initio calculations. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 9371-9383 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The theory of constructing diabatic electronic wave functions for strongly coupled potential energy surfaces is briefly reviewed. The use of a particularly simple diabatization scheme is advocated which removes only the leading terms of the nonadiabatic, or derivative, coupling elements. It is tested numerically for a well-established E⊗e Jahn–Teller problem and shown to lead to very good (often excellent) agreement with the exact results. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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