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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 3458-3476 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This series is concerned with the quantum dynamics of overtone relaxation in planar benzene and in reduced mode planar benzene fragments. In these studies, ultralarge direct product primitive vibrational spaces (of dimension up to 1010) are contracted to active spaces of dimension 5000–10 000. The contractions are carried out via artificial intelligence tree pruning algorithms, or a new iterative wave operator pruning algorithm. The exact dynamics within the active space is then developed via the recursive residue generation method. In part I of this series, emphasis is placed upon v=3 CH overtone dynamics in the 5 and 9 mode benzene fragments C3H and C3H3. Neither system undergoes complete relaxation, but the survival probability in C3H undergoes large amplitude oscillations with a period characteristic of stretch–wag interaction in the CH chromophore. For C3H3, the two initially nonexcited CH stretch modes do not play a significant role in the dynamics for t〈1 ps. However, modes in both systems that have a high degree of wag motion for the initially excited chromophore play a significant role at short times. Comparisons with earlier classical trajectory studies show good correspondence between the classical and quantum results only at short times, t〈0.1 ps.
    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 97 (1992), S. 2481-2489 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a study of the intramolecular vibrational energy redistribution (IVR) from a highly excited C–H overtone of the CD3H molecule. The whole vibrational manifold has been explicitly considered in the calculations. Two different approaches have been used and compared. In a direct approach, we have kept all the states located below a given threshold energy, resulting in a basis set of 92 000 states. The second approach consisted in selecting the important states in order to define a dynamically relevant active space (AS) of much lower size (≈2000). The two approaches were first applied to the calculation of the n=6 C–H overtone spectrum, showing that the AS method is quite able to reproduce the exact results. More stringent test concerned the actual time evolution of the C–H stretch local mode ||6ν1(approximately-greater-than)0. Explicit time propagation has been carried out in the larger basis set, over a 15 ps interval. Results show that the dynamics is mainly governed by a few resonant states involving the C–H bending and C–D stretching motions. Very slow relaxation out of the C–H chromophore is observed over this 15 ps period. The AS method, using a much smaller basis set, was shown to reproduce the correct behavior of the C–H chromophore dynamics during the first 2 ps.
    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 94 (1991), S. 7311-7318 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The method presented here is based on the solution of the time-dependent complex-scaled Schrödinger equation to provide the complex-scaled evolution operator after one optical cycle. This method is mainly suitable in the study of multiphoton ionization or dissociation under the influence of high intense fields. An illustrative numerical example is given.
    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 94 (1991), S. 6388-6397 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A grid formulation is presented for the body-fixed (BF) motion of a rotating triatomic molecule. The BF component of the wave function, described in terms of Jacobi coordinates, is discretized on a {Ri×rj×θα} grid. By use of the generalized discrete variable representation (DVR) of Light, Hamilton, and Lill [J. Chem. Phys. 82, 1400 (1985)] one can employ the same θ grid for the different Ω components of the wave function, Ω corresponding to the projection of the total angular momentum J onto the z BF axis. Such a unique grid definition allows one to define adiabatic states, with respect to the θ coordinate, independent of the Ω value considered. These states have been directly computed by means of a distributed 2D DVR, sampling only the relevant points in configuration space. Further reduction of the rovibrational basis set was achieved by defining new adiabatic states, with respect to the Ω component. This formation is applied to the calculation of bound rovibrational states of the HCN molecule for the J=2 value.
    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 92 (1990), S. 227-230 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The resonances obtained by a method, which is based on the original work of Datta and Chu [Chem. Phys. Lett. 87, 357 (1982)] and of Schneider [Chem. Phys. Lett. 31, 237 (1975); Phys. Rev. A 11, 1957 (1975)], are studied for a one-dimensional model, for a two-dimensional model suggested by Chu, describing rotational predissociation in van der Waals complexes, and for the variational predissociation of Ne–ICl in the adiabatic approximation for a potential surface given by Delgado-Barrio and Villarreal (to be published). The resonance positions and widths are associated with the complex eigenvalues of a complex matrix obtained by a product of three matrices St H S, where H is the Hermitian Hamiltonian matrix, and S is an overlap matrix between complex scaled and unscaled basis functions. The method has the advantage of being applicable to potentials given numerically on the real axis. It also avoids the need to construct a new complex Hamiltonian matrix for each scaling angle, as is the case in the complex coordinate method.
    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 92 (1990), S. 247-253 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present an exact three-dimensional quantum study of the dissociation of the ozone molecule on a single potential-energy surface (1B2). The wave function has been discretized on a three-dimensional grid, in conjunction with a mixed pseudospectral scheme in order to represent the action of the Hamiltonian operator on it. The correlation function (Fourier transform of the total cross section) has been computed within the time formulation. This function was obtained by means of the Lanczos algorithm, without any actual propagation of the initial wave packet on the upper surface. A calculation performed for the total angular momentum value J=0, reproduces the characteristic features of the experimental correlation function (recurrence times).
    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 90 (1989), S. 3198-3203 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present in this paper an application of the Lanczos algorithm to the fitting of a potential energy surface from the experimental spectrum. This method presents two definite improvements on the conventional approach: (i) the Lanczos algorithm allows to treat ultra-large basis sets (120 000 states in this calculation) and (ii) it is possible to tune selectively the calculation to specific components of the spectrum (e.g., a given combination band nνi+mνj) thus reducing considerably the complexity of the fit. This method has been applied to the CD3H molecule, considering all the vibrational degrees of freedom. Converged line positions have been obtained for high overtones of the C–H stretching mode (up to 16 000 cm−1). The accuracy of the fitted surface is demonstrated by direct comparison of experimental and calculated spectroscopical parameters.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 6836-6840 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Resonance transition probabilities are obtained without the need to compute eigenvectors of the complex scaled Hamiltonian matrix. The new computational approach is a combination of the complex Lanczos recursion method, the complex coordinate method, and the extension of the Wyatt and Scott modified QL algorithm to complex matrices. To illustrate the method, the coupling strength between a resonance state and different scattering channels of HD from a flat Ag surface are calculated.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 3477-3486 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This series is concerned with the quantum dynamics of overtone relaxation in benzene and in reduced mode benzene fragments. In part II of this series, emphasis is placed upon time-dependent studies of v=3 CH overtone relaxation in a 16 mode planar benzene model (5 CH stretch modes are inactive out of the 21 planar modes). Through use of the wave operator contraction algorithm, primitive vibrational basis sets containing up to 1.1×109 states are contracted to active spaces of dimension about 4000 states. The exact dynamics within the active space is developed with the recursive residue generation method. The time-dependent survival probability of the CH(v=3) overtone is compared with results from classical mechanics and with the Fourier transform of the experimental overtone spectra. The classical and quantum results are in good agreement only at short times (t〈0.1 ps). At longer times multiple small recurrences are present in the quantum results. The quantum and experimental results share common features (rapid falloff at short times, followed by multiple small recurrences), but there are quantitative differences. The sensitivity of the quantum survival to alterations in the anharmonic potential is also studied. The short-time dynamics (t〈0.5 ps) is shown to be accurately reproduced by reduced 4 and 5 mode models. Only a small subset of states in these carefully selected modes are significantly populated during the early decay of the v=3 overtone, even though the total density of states is very large.
    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 97 (1992), S. 4255-4263 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A methodology for the calculation of high energy vibrational eigenstates of S0 acetylene is described. Acetylene is modeled as a 5D planar molecule. The discrete variable representation (DVR) is employed for radial coordinates with a finite basis representation (FBR) for the angular coordinates. Symmetry adaptation of the primitive basis (dimension 2.7 × 106) coupled with a two level diagonalization/truncation scheme maintains relatively small basis sets (〈 2500 functions) in all diagonalizations. Eigenvalues up to nearly 3700 cm−1 above the ground state are reported.
    Type of Medium: Electronic Resource
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