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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 7901-7909 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a new complex-scaling Fourier-grid Hamiltonian (CSFGH) method for accurate and efficient determination of laser-induced (multichannel) molecular resonance states without the use of basis set expansions. The method requires neither the computation of potential matrix elements nor the imposition of boundary conditions, and the eigenvectors provide directly the values of the resonance wave functions at the space grid points. The procedure is particularly valuable for excited-state problems where basis set expansion methods face the challenge. The simplicity and usefulness of the CSFGH method is demonstrated by a case study of the intensity-dependent complex quasivibrational energy eigenvalues (ER, −Γ/2) and eigenvectors associated with multiphoton and above-threshold dissociation of H+2 ions in the presence of intense laser fields (I=1012–1014 W/cm2 ).
    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 88 (1988), S. 6233-6239 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The S-matrix version of the Kohn variational principle is used to obtain a very effective method for quantum scattering calculations. The approach is especially useful for the nonlocal (i.e., exchange) interactions that arise in chemically reactive scattering (and also in electron–atom/molecule scattering). The particular version developed in this paper has a more general structure than an earlier one by Miller and Jansen op de Haar [J. Chem. Phys. 86, 6213 (1987)], and applications to an elastic scattering problem, and also to three-dimensional H+H2 reactive scattering, show that it is also more useful in practice.
    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 86 (1987), S. 3225-3238 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a practical nonperturbative method for exact treatment of intensity-dependent generalized nonlinear optical susceptibilities χ(ω) in intense polychromatic fields, valid for arbitrary laser intensities, detunings, and relaxation. By means of the many-mode Floquet theory, the time-dependent Liouville equation can be transformed into an equivalent time-independent infinite-dimensional Floquet–Liouville supermatrix (FLSM) eigenvalue problem. It is then shown that the nonlinear optical susceptibilities χ(ω) can be completely determined simply from the supereigenvalues and eigenfunctions of the Floquet–Liouvillian LˆF. In addition to this exact FLSM approach, we have also presented higher-order perturbative results, based on the extension of the Salwen's nearly degenerate perturbation theory, appropriate for somewhat weaker fields and near-resonant multiphoton processes, but beyond the conventional perturbative or rotating wave approximation (RWA). In the case of two-level systems, for example, the implementation of Salwen's method in the time-independent LˆF allows the reduction of the infinite-dimensional FLSM into a 4×4 dimensional effective Hamiltonian, from which essential analytical formulas for intensity-dependent χ(ω) can be obtained. These methods are applied to a detailed study of intensity-dependent spectral line shapes (such as hole burning and extra resonance peaks at the line center, and the effects of saturation, detuning, and radiative and collisional damping, etc.) and subharmonic structures in nonlinear multiple wave mixings χ[(m+1)ω1−mω2] for two-level systems in intense linearly polarized bichromatic fields.
    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 85 (1986), S. 1403-1411 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We extend the inhomogenous-differential-equation (IDE) approach of Dalgarno and Lewis for a detailed study of two-photon dissociation (TPD) of HD+ from high vibrational levels of the 1sσg electronic state. Contrary to the H+2 case, where the TPD cross sections σ(2)L are largest near TPD thresholds and decrease monotonically with increasing photon energy, the HD+ cross sections are characterized by rich resonant and interference structures. We present σ(2)L results for TPD from the initial vi =6, 8, 10, 12, 14, 16, and ji=0 levels as well as from vi=14, ji=0, 2, 4 levels for a wide range of wavelengths of linearly polarized radiation accessible by CO2 and CO lasers. It is found that while there are four TPD pathways, the channel 1sσg(vi ji)→ω 1sσg(v, j=ji±1) →ω2pσu(k, j f=j±1) dominates the two-photon process in most of the cases we have studied. Further, the results show that σ(2)L increases rather rapidly as the initial vibrational quantum number vi increases, indicating that the hereronuclear diatomic molecules in high vibrational levels can be efficiently two-photon dissociated by IR lasers. Consequently molecular structures near the dissociation limit may be conveniently probed by two-photon spectroscopy—as has indeed been demonstrated recently by experiments. Our σ(2)L results thus provide complementary information to the HD+ spectroscopic data obtained recently by Carrington et al.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 129-146 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several recent extensions of the method of complex scaling to the studies of autoionization, predissociation, and multiphoton dynamics will be presented. Specific subjects to be discussed include: 1Complex-coordinate coupled-Landau-channel method for autoionizing resonances and photoinization of atomic hydrogen in intense magnetic fields,2Non-Hermitian complex quasi-energy method for multiphoton dissociation of small molecules with specific application to two-photon dissociation of vibrationally excited H2+ and HD+, and3Vibrational predissociation of highly vibrationally excited He - I2* (v) van der Waals molecules.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 69 (1998), S. 305-315 
    ISSN: 0020-7608
    Keywords: Floquet theory ; time-dependent density functional theory ; multicolor laser fields ; multiphoton ionization ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We generalize the Floquet formulation of the time-dependent density functional theory (TDDFT) [Telnov and Chu, Chem. Phys. Lett. 264, 466 (1997)] to the case of many-electron systems in multicolor or polychromatic time-dependent fields. It is shown that the time-dependent Kohn-Sham equations can be transformed into an equivalent time-independent infinite-dimensional Floquet Hamiltonian eigenvalue problem. For the case of bound-free transitions, we introduce the notion of complex density and present a non-Hermitian many-mode Floquet formulation of TDDFT. A procedure is presented for the determination of the complex quasi-energies and the calculation of the total and partial ionization rates from individual electron orbitals. The theory is illustrated by a case study of multiphoton ionization of He atoms in the presence of an intense 248 nm laser field and its third harmonic. Novel intensity- and phase-dependent behavior of multiphoton processes in two-color fields is reported.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 305-315, 1998
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0020-7608
    Keywords: Time-dependent density functional theory ; optimized effective potential ; multiphoton processes ; high-order harmonic generation ; self-interaction correction ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We present a time-dependent density-functional theory (TDDFT) with optimized effective potential (OEP) and self-interaction correction (SIC) for nonperturbative treatment of multiphoton and nonlinear optical processes of many-electron systems in intense laser fields. The resulting TDOEP/KLI-SIC equations are structurally similar to the time-dependent Hartree-Fock equations but include the many-body effects through an orbital-independent single-particle local time-dependent exchange-correlation (xc) potential. The method is applied to the all-electron study of the coherent control of multiple high-order harmonic generation (HHG) of He atoms in two-color mixed laser fields. A generalized pseudospectral time propagation method is introduced for efficient and accurate solution of the TDOEP/KLI-SIC equations in three spatial dimensions. It is found that the mixing of a strong second-harmonic (527 nm) field with a weak fundamental (1053 nm) field can lead to the production of both odd and even harmonics simultaneously with relatively high yield. Further, the relative efficiency of the HHG production can be controlled by varying the relative polarization of the two laser beams. The theoretical predictions are in accord with recent experimental observations.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 293-303, 1997
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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