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  • 1
    Electronic Resource
    Electronic Resource
    Quantum control of nuclear wave packets by locally designed optimal pulses (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 9318-9331 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new approach to locally design a control pulse is proposed. This locally optimized control pulse is explicitly derived, starting with optimal control formalism, and satisfies the necessary condition for a solution to the optimal control problem. Our method requires a known function, g(t), a priori, which gives one of the possible paths within the functional space of the objective functional. A special choice of g(t)≡0 reduces the expression of the control pulse to that derived by Kosloff et al. For numerical application, we restrict ourselves to this special case; however, by combining an appropriate choice of the target operator together with the backward time-propagation technique, we apply the local control method to population inversion and to wave packet shaping. As an illustrative example, we adopt a two-electronic-surface model with displaced harmonic potentials and that with displaced Morse potentials. It is shown that our scheme successfully controls the wave packet dynamics and that it can be a convenient alternative to the optimal control method for wave packet shaping. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477593
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  • 2
    Electronic Resource
    Electronic Resource
    Theoretical study of bath-induced coherence transfer effects on a time- and frequency-resolved resonant light scattering spectrum. II. Energy mismatch effects (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 8321-8331 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Bath-induced coherence transfer effects on a time- and frequency-resolved resonant light scattering spectrum is theoretically investigated using the Markoff master equation. According to Eberly and Wódkiewicz, a general expression for an experimentally observable spectrum in terms of a molecular response function is derived within the density matrix formalism. To generalize our previous results of the bath-induced coherence transfer which were derived based on a displaced harmonic oscillator model [Y. Ohtsuki and Y. Fujimura, J. Chem. Phys. 91, 3903 (1989)], an eigenstate basis is used to represent a relevant system for investigating characteristics of the transfer. By the present model, we clarify the dependence of the bath-induced coherence transfer on the energy-level structure of the intermediate states associated with the transfer, i.e., energy mismatch effects. It is shown that if the energy mismatch of these states is smaller than dephasing rates, the bath-induced coherence transfer occurs resonantly. In the other cases, the energy mismatch brings about a modulation in the time evolution of the superposition state created by the bath-induced coherence transfer, which strongly diminishes the efficiency of the transfer. The resonance condition is derived analytically and is confirmed by numerical calculations of quantum beats induced by the bath-induced coherence transfer. The possibility of very rapid dephasing of a quantum beat signal which cannot be explained in terms of dephasing rates is also shown, when the transition moments have such values that give π-phase-shifted quantum beats in bath-induced fluorescence. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471603
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  • 3
    Electronic Resource
    Electronic Resource
    Control of quantum dynamics by a locally optimized laser field. Application to ring puckering isomerization (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 5646-5655 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We presented a theoretical method for controlling quantum dynamics by locally optimized nonstationary laser fields, within the semiclassical theory of the molecule–radiation field interaction. The external laser field is optimized based on the control theory of a linear time-invariant (LTI) system, so that both the summation of the population of the nontarget states and the total energies of the laser fields are minimized. The optimization procedure involves operation of the so-called feedback gain matrix to the time-dependent state vector. This procedure is carried out at every successive short stage, in which the time-dependent Schrödinger equation can be approximated to the equation of motion of the LTI system. As an example, the control theory was applied to laser-induced ring-puckering isomerization, the dynamics of which can be described as the wave packet in the one-dimensional double minimum potential under locally optimized laser fields. The result indicated that nearly 100% of the population can be transferred to the final product state by irradiation of the optimized laser fields. The optimized laser fields were analyzed to obtain information on the carrier frequencies or the frequency modulation by using the fast Fourier transform method. These results were then compared with the result of isomerization induced by nonoptimized laser fields.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467132
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  • 4
    Electronic Resource
    Electronic Resource
    Numerical simulation of the isomerization of HCN by two perpendicular intense IR laser pulses (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 9083-9092 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Isomerization of HCN is studied numerically for a laser excitation configuration of two perpendicular intense IR pulses. This scheme confines the molecule to a plane and promotes proton transfer along the curved reaction path. It is shown that internal rotation of the CN group enhances isomerization when compared to a fixed C≡N orientation model. Isomerization rates with rotation exceed those without rotation of the CN by about a factor of 3. Internal rotation also enhances dissociation and destroys phase control of the isomerization. It is found that at intensities I∼1013 W/cm2, maximum isomerization occurs with negligible dissociation for a 2 ps pulse excitation. Maximum isomerization is also found for one field frequency resonant with the CH bend frequency ωbend and the other perpendicular frequency at 2ωbend. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472742
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  • 5
    Electronic Resource
    Electronic Resource
    Theory of quantum beats in time-resolved multiphoton ionization of molecules (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 1501-1510 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An expression for the probability of time-resolved three-photon ionization via coherently excited resonant states of a molecular system is derived in the perturbative density matrix formalism with the aid of the Liouville space Feynman diagram. It is shown how the time evolution of the molecular coherence in the first resonant state can be detected as a function of the delay time between the pumping and probing lasers through the probing two-photon ionization process. The three-photon ionization process consists of the simultaneous and sequential processes which are classified by the Liouville space Feynman diagrams. The possibility of appearance of quantum beats in the pump–probe three-photon ionization is discussed by performing model calculations of the probability of ionization. The role of the direct and redistributed processes is discussed. The redistributed process is induced by intramolecular processes in the resonant state. The theoretical treatment is applied to the (1+2) three-photon ionization of pyrazine observed by Knee et al. It is demonstrated that the fast decay component (110 ps) of the pyrazine spectra originates from the intramolecular dephasing of the vibronic coherence created by the pumping pulse laser, and this component appears only when the redistributed process (the ionization process through triplet levels) is absent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454128
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  • 6
    Electronic Resource
    Electronic Resource
    Application of the indirect dephasing model to resonance and dispersed fluorescence in the isolated molecular complex (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 2510-2517 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The theory of indirect dephasing proposed by Hiroike is applied to studying the mechanism of line broadening in resonance and dispersed fluorescence spectra of molecular complexes in supersonic free jet. In the indirect dephasing model, the width of the luorescence spectra which is characterized by the homogeneous linewidth can be expressed in terms of two parameters, the rate of intramolecular vibrational redistribution (IVR), γ and frequency change induced by the IVR, δω. It is shown that the non-Markovian character introduced into the interaction between the intra- and intermolecular modes reduces the indirect dephasing rate. The theory is applied to calculation of the linewidth of the resonance fluorescence of the tetrazine–Ar molecular complex excited in 6a1 vibronic level. The introduction of the non-Markovian character is necessary to calculate the linewidth of the fluorescence in a molecular complex with a few intermolecular modes such as tetrazine–Ar.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452103
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  • 7
    Electronic Resource
    Electronic Resource
    Theory of vibrational predissociation of van der Waals complex in the adiabatic approximation model (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 7106-7116 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theory of the vibrational predissociation (VPD) of linear triatomic van der Waals (vdW) complexes in the adiabatic approximation model is developed aiming to evaluate the VPD rates from higher quantum states as well as the lowest one of the initially excited intramolecular vibrational mode. The adiabatic wave functions of the high frequency intramolecular mode and the adiabatic potential curves are constructed from a Morse-type interaction potential between the two neighboring atoms of the vdW bond. Using Fermi's Golden Rule, expressions for the rate of the VPD are derived both in the Condon approximation and in the non-Condon scheme. Important contribution of the non-Condon scheme in the adiabatic approximation model is demonstrated by performing model calculations of the VPD rate constants of I2X vdW complexes. The magnitudes of the rate constant in the Condon approximation are smaller than those in the non-Condon scheme by about one to two orders. It is shown that there is a good correspondence in the vibrational quantum number dependence between the treatment in the adiabatic approximation model and that in the scattering theory based on the zero-order diabatic basis set derived by Beswick and Jortner, and that the magnitudes of the vibrational predissociation rate constant calculated by them exist between those in the Condon approximation and in the non-Condon scheme. An approximate expression for the potential displacements between two adiabatic potentials and that for the intramolecular frequency shifts are also derived.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451397
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  • 8
    Electronic Resource
    Electronic Resource
    Locally designed pulse shaping for selective preparation of enantiomers from their racemate (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 1575-1581 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a method for the design of laser fields to control a selective preparation of enantiomers from their racemate. An expression for two components of the laser pulses [EX(t) and EY(t)] propagating along the Z axis is derived using a locally optimized control theory in the density operator formalism. This expression was applied to a selective preparation of (R-, L-) enantiomers from preoriented phosphinotioic acid (H2POSH) at low temperatures. The target operator was set for the populations to be localized in one side of the double-well potential. First, a simple one-dimensional model was treated. Then, a two-dimensional model in which a free rotation around the preoriented torsional axis is included was briefly considered. In the one-dimensional model, almost complete preparation of the enantiomers was obtained. The optimal electric field consists of a sequence of two linearly polarized pulses with the same phases but with different magnitudes. This means that the resultant electric field is linearly polarized with the polarization for obtaining the R-form nearly parallel to its S–H bond. The optimal electric field transfers the L-form into the R-form while suppressing the reverse process. In the two-dimensional model, the enantiomer selective preparation is controlled by a sequence of circularly polarized pulses. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1334867
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  • 9
    Electronic Resource
    Electronic Resource
    Resonance Raman scattering from molecules with a nonequilibrium vibronic distribution (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 1246-1254 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Expressions for the differential cross section of the resonance Raman scattering from molecules in which initially prepared nonequilibrium vibronic levels undergo vibrational and/or electronic relaxations are derived by using the generating function method. Two kinds of the initial nonequilibrium vibronic distributions, single vibronic level and Poisson ones are taken into account. A displaced harmonic oscillator model for the initial and resonant vibrational states and a linear vibrational quantum number dependence of the relaxation constants are adopted in deriving the cross sections. Model calculations of the time-resolved resonance Raman scattering cross sections and of the excitation profiles of the nth order Stokes and anti-Stokes Raman bands are performed by using the derived expressions. The results of the calculation indicate that the anti-Stokes Raman bands make a significant contribution to the resonance Raman scattering from the nonequilibrium vibronic distributions. It is suggested that measurements of the excitation profiles are useful for analyzing the nonequilibrium distribution initially prepared and the subsequent relaxation mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448445
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  • 10
    Electronic Resource
    Electronic Resource
    Non-Markoffian theory of quantum beats in molecular fluorescence (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 2112-2119 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We develop a theory of quantum beats in molecular fluorescence taking into account collision effects (such as pure dephasing due to elastic collision) without invoking the Markoff approximation. Model calculations of the time dependent fluorescence from molecules with two excited levels are performed in order to see how the non-Markoffian character in the collision process exerts influence upon the quantum beat pattern. It is suggested that if the pure dephasing between the excited states is a Markoffian "the degree of modulation of the beats'' decreases exponentially with time; if it is in the static limit the degree of modulation of the beats decreases as a Gaussian function (the non-Markoffian behavior in the quantum beats). A given case can be classified as either Markoffian or non-Markoffian, depending on the relative magnitudes of the collision duration time τc, the beat frequency ω, and the coupling strength v which is characteristic of the pure dephasing process. The Markoff approximation holds only if the condition ω〈v〈1/τc is satisfied; the non-Markoffian behavior appears in the quantum beat pattern when ω〉v, even if v2τ2c〈1 .
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450422
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