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  • 1
    Electronic Resource
    Electronic Resource
    Thermal dimerization of 1-substituted-3,4-dimethylphospholes within the coordination sphere of platinum(II) (1994)
    s.l. : American Chemical Society
    Inorganic chemistry 33 (1994), S. 109-117 
    Details
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ic00079a021
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  • 2
    Electronic Resource
    Electronic Resource
    Quantum mechanics in phase space: New approaches to the correspondence principle (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 8862-8874 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a time evolution equation that provides a novel basis for the treatment of quantum systems in phase space and for the investigation of the quantum-classical correspondence. Through the use of a generalized Husimi transform, we obtain a phase space representation of the time-dependent Schrödinger equation directly from the coordinate representation. Such an equation governs the time evolution of densities such as the Husimi density entirely in phase space, without recourse to a coordinate or momentum representation. As an application of the phase-space Schrödinger equation, we compute the eigenfunctions of the harmonic oscillator in phase space, relate these to the Husimi transform of coordinate representation eigenstates, and investigate the coherent state, its time evolution, and classical limit ((h-dash-bar)→0) for the probability density generated by this state. Finally, we discuss our results as they relate to the quantum-classical correspondence, and quasiclassical trajectory simulations of quantum dynamics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459225
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  • 3
    Electronic Resource
    Electronic Resource
    Ring torsional dynamics and spectroscopy of benzophenone: A new twist (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 2169-2184 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The low energy portion of the high resolution S1←S0 fluorescence excitation spectrum of benzophenone recently reported by Holtzclaw and Pratt [J. Chem. Phys. 84, 4713 (1986)] is modeled here using a simple two-degree-of-freedom vibrational Hamiltonian. The Hamiltonian features a 1:1 nonlinear resonance between the two low frequency ring torsional modes of the molecule in its S1 state. Line positions and intensities of the two major spectral progressions are well reproduced using parameters similar to those derived from earlier matrix diagonalizations. The comparison of the theory and experiment results in a determination of the displacement of the S1 surface relative to the ground electronic state along the symmetric torsional coordinate and permits a calculation of the excitation spectra of various isotopically substituted molecules not yet measured in the laboratory. A clear picture of the relationship between the dynamics on the S1 surface and the spectroscopy of benzophenone is revealed by comparing a time domain analysis of the experimental data with wave packet dynamics on the model S1 surface. This comparison provides new insight into energy flow in the isolated molecule and permits a qualitative simulation of the effects of collisional quenching on the fluorescence spectrum. We also discuss, using a classical trajectory analysis, the resonance dynamics of the torsional modes and note the existence of heretofore undetected local modes in the high resolution spectrum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454050
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  • 4
    Electronic Resource
    Electronic Resource
    Multidimensional quantum eigenstates from the semiclassical dynamical basis set (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 6592-6608 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new method for obtaining molecular vibrational eigenstates using an efficient basis set made up of semiclassical eigenstates is presented. Basis functions are constructed from a "primitive'' basis of Gaussian wave packets distributed uniformly on the phase space manifold defined by a single quasiperiodic classical trajectory (an invariant N-torus). A uniform distribution is constructed by mapping a grid of points in the Hamilton–Jacobi angle variables, which parametrize the surface of the N-torus, onto phase space by means of a careful Fourier analysis of the classical dynamics. These primitive Gaussians are contracted to form the semiclassical eigenstates via Fourier transform in a manner similar to that introduced by De Leon and Heller [J. Chem. Phys. 81, 5957 (1984)]. Since the semiclassical eigenstates represent an extremely good approximation of the quantum eigenstates, small matrix diagonalizations are sufficient to obtain eigenvalues "converged'' to 4–5 significant figures. Such small diagonalizations need not include the ground vibrational state and thus can be used to find accurate eigenstates in select regions of the eigenvalue spectrum. Results for several multidimensional model Hamiltonians are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453444
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  • 5
    Electronic Resource
    Electronic Resource
    S1–S2 vibronic coupling in trans-1,3,5-hexatriene. II. Theoretical investigation of absorption and resonance Raman spectra (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 626-640 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: No direct absorption or emission signals of the 2 1Ag state of trans-1,3,5-hexatriene (THT) have been detected so far. However, the ab initio calculations of the three valence singlet states of THT presented in the preceding paper (paper I) put the vertical excitation energy of the 2 1Ag state ca. 0.5 eV below that of the 1 1Bu state. This result indicates possible strong vibronic coupling effects on the spectroscopy of the bright 1 1Bu state. We construct a quantum-mechanical three-state eight-mode model Hamiltonian operator for the microscopic description of the ultrafast S2→S1 internal conversion dynamics following optical excitation of the 1 1Bu state based on the ab initio potential energy information for the S0, S1, and S2 states of THT compiled in paper I. This dynamical model is shown to yield a reliable description of the absorption, preresonance and resonance Raman (RR) spectroscopy of the 1 1Bu state of THT. The homogeneous linewidth of 155 cm−1 FWHM observed for the origin band of the 1 1Ag→11Bu transition can be reproduced with an optical dephasing time T2 of 90 fs. The strong enhancement of 1 1Bu RR bands involving the almost Franck–Condon inactive tuning mode ν9 as well as the observed rapid 1 1Bu population decay indicate that the S1 and S2 states are probably nearly degenerate, the 2 1Ag energy may also be slightly higher than that of the 1 1Bu state vertically. However, the parameter set that yields a realistic description of the RR spectroscopy and population dynamics within the eight-mode vibronic coupling model needs to be modified in order to reproduce the high-resolution 1 1Bu absorption profile, i.e., a significant reduction of the ab initio interstate coupling constants is required. A convergence of the two different parameter sets can be expected if the Hamiltonian is extended by the 28 weakly coupled modes that are considered by a phenomenological relaxation term in the present model. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480554
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  • 6
    Electronic Resource
    Electronic Resource
    Classical trajectory study of vibration-rotation interaction in highly excited triatomic molecules (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 190-207 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: For two qualitatively different model triatomic molecules, SO2 and "bent equilibrium OCS,'' classical trajectory calculations of the rotational and vibrational motion are presented for microcanonical ensembles of initial conditions at 35% to 85% of a bond dissociation energy. At the higher energies, many of the trajectories exhibit substantial intramolecular vibrational-rotational energy transfer (IVRET), which has a significant effect on the geometry of rotational motion including in some cases, a transition between the two types of stable asymmetric top motion. IVRET is caused principally by centrifugal interactions, and in "bent OCS,'' it is dominated by a 2:1 resonance. The rotational motion of about half of the high energy SO2 trajectories is essentially statistical, but bent OCS never undergoes statistical IVRET.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449808
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  • 7
    Electronic Resource
    Electronic Resource
    S1–S2 vibronic coupling in cis-1,3,5-hexatriene. I. Electronic structure calculations (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 1631-1644 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The estimates for the vertical excitation energy of the 2 1A1 state of cis-1,3,5-hexatriene (CHT) vary considerably and provide a good example of the difficulties that can arise in determining transition energies. The great uncertainty is surprising if one considers that this state has already been characterized by high resolution techniques such as resonance enhanced multiphoton ionization (REMPI) and fluorescence excitation spectroscopy in free jet expansions. A theoretical analysis of this problem is clearly needed and the present work, along with the following paper, represents an effort to investigate the nature of the 2 1A1 and 1 1B1 states of CHT. It is shown that a combination of ab initio electronic structure and quantum-mechanical wave packet calculations is required to systematically approach a question as involved as locating the energetical position of the 2 1A1 level. We characterize the energy dependence of the 1 1A1, 2 1A1, and 1 1B1 states of CHT as a function of the in-plane normal coordinates for small displacements from the ground-state equilibrium geometry employing the single-state multiconfigurational second-order perturbation theory (CASPT2) method. This information constitutes the basis for the construction of diabatic harmonic model potential-energy functions associated with the three electronic states in the Franck–Condon region that is essential for the treatment of nonadiabatic dynamics. Five totally symmetric modes with high Franck–Condon and/or tuning activity are identified. Vibronic interaction between the S1 and S2 states is primarily mediated by four vibrations of b1 symmetry, ν26, ν27, ν30, and ν31. ν30 and ν31 are found to be exceptionally powerful interstate coupling modes and the strong nonadiabatic effects induced by these modes in CHT are mainly responsible for the spectroscopic differences observed for the S1 and S2 states of CHT and trans-1,3,5-hexatriene. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1333708
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  • 8
    Electronic Resource
    Electronic Resource
    S1–S2 vibronic coupling in cis-1,3,5-hexatriene. II. Theoretical investigation of absorption and resonance Raman spectra (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 1645-1662 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A wave packet prepared on the 1 1B1 potential-energy surface of cis-1,3,5-hexatriene (CHT) is characterized by a very short lifetime of (approximate)20 fs in this state. We present here model calculations of the excited-state dynamics of CHT that are consistent with the experimentally determined population decay time scale and yield an accurate description of the absorption, preresonance and resonance Raman (RR) spectroscopy of the 1 1B1 state. The greater diffuseness and complexity of the free jet 1 1B1 absorption band of CHT as compared to the 1 1Ag→1 1Bu transition of trans-1,3,5-hexatriene can be explained by a faster optical dephasing rate and more densely spaced vibronic level structure in the S2 state of the cis isomer primarily due to the presence of two very active low-frequency S1–S2 coupling modes, ν30 and ν31. The first measurement of the one-photon 1 1A1→2 1A1 transition of CHT has been reported only ten years ago and the S1 state has since been thoroughly studied by different techniques. The simulations of the excitation and RR emission profiles of the 2 1A1 state performed for this work are shown to be in quantitative agreement with the observed spectra. One of the most important and controversial questions arising from the spectroscopic information about the 2 1A1 state concerns the nature of the intensity carrier for the one-photon S0→S1 excitation process. It can be shown that the oscillator strength for one-photon transitions into the 2 1A1 vibronic manifold is exclusively borrowed from the electronic 1 1B1 configuration. One model Hamiltonian is defined for the representation of wave packet motion in the 1 1A1, 2 1A1, and 1 1B1 states and the nuclear coordinate space comprises eight dimensions. The relevant normal modes are either of a1 or b1 symmetry, i.e., only first-order intrastate or S1–S2 vibronic coupling effects are considered, and have been selected based on the electronic structure information compiled in the preceding paper. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1333709
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  • 9
    Electronic Resource
    Electronic Resource
    S1–S2 vibronic coupling in trans-1,3,5-hexatriene. I. Electronic structure calculations (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 613-625 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The potential-energy surfaces of the 1 1Ag, 2 1Ag, and 1 1Bu states of trans-1,3,5-hexatriene (THT) are explored in the vicinity of the ground state equilibrium structure. The S0 geometry optimization and force field calculation have been carried out with the restricted Hartree–Fock plus Møller–Plesset second-order perturbation theory method. Vibronic coupling constants for the normal coordinates of ag and bu symmetry were computed with the complete-active-space self-consistent-field (CASSCF) and single state multiconfigurational second-order perturbation theory (CASPT2) electronic structure models. The CASSCF/CASPT2 method unequivocally places the vertical excitation energy of the dark 2 1Ag "phantom state" below the 1 1Bu level and predicts an energy difference of ca. 0.5 eV. The results are consistent with time-resolved photoionization yield and photoelectron spectroscopy experiments that indicate the existence of a low lying S1–S2 conical intersection which induces rapid 1 1Bu→2 1Ag internal conversion on a time scale of 40 fs to 50 fs [Cyr and Hayden, J. Chem. Phys. 104, 771 (1996)]. Based on the vibronic coupling constants five totally symmetric vibrations with high Franck–Condon and/or tuning activity have been identified. The S1 and S2 states interact primarily via the two bu normal modes ν24 and ν26. Other ag and bu normal vibrations do not appear to couple significantly to the lowest lying π→π* transition. The modeling of the ultrafast relaxation processes following optical excitation of the 1 1Bu state of THT and the calculation of absorption and resonance Raman spectra are discussed in the following paper. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480553
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  • 10
    Electronic Resource
    Electronic Resource
    General formulation of the vibrational kinetic energy operator in internal bond-angle coordinates (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 7255-7271 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A general formulation of the vibrational kinetic energy operator expressed in internal bond-angle coordinates is presented. This formulation is based on Podolsky's expression for the covariant form of the Laplace–Beltrami operator. When a valid set of internal bond-angle coordinates is employed, it is possible to adapt a systematic approach to solve for the Jacobian determinant governing the coordinate transformation from Cartesian coordinates. In the general case of an arbitrary N-atom system, this Jacobian always factorizes to a simple form. This allows one to evaluate all the terms that contribute to V(circumflex)′, the effective potential that arises from transforming the kinetic energy operator to internal coordinates. We discuss restrictions on the choice of internal vibrational coordinates that may be included in a valid set. We then provide tabular information from which the vibrational kinetic energy operator for any molecular system can be constructed directly with no matrix inversion or chain rule manipulation required. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480101
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