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  • 1
    Electronic Resource
    Electronic Resource
    Adiabatic time evolution of atoms and molecules in intense radiation fields (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2657-2665 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We derive the condition for a time dependent quantum system to exhibit an exact or higher order adiabatic time evolution. To this end, the concept of adiabaticity is first analyzed in terms of the transformation properties of the time-dependent Schrödinger equation under a general unitary transformation Uˆ(t). The system will follow an adiabatic time evolution, if the transformed Hamiltonian, Kˆ(t)=Uˆ°HˆUˆ−i(h-dash-bar)Uˆ°Uˆ, is divisible into an effective Hamiltonian hˆ(t), defining adiabatic quasistationary states, and an interaction term Ωˆ(t), whose effect on the adiabatic states exactly cancels the nonadiabatic couplings arising from the adiabatic states' parametric dependence on the time. This decoupling condition, which ensures adiabaticity in the system's dynamics, can be expressed in a state independent manner, and governs the choice of the unitary operator Uˆ(t), as well as the construction of the effective Hamiltonian hˆ(t). Using a restricted class of unitary transformations, the formalism is applied to the time evolution of an atomic or molecular system in interaction with a spatially uniform electromagnetic field, and gives an adiabatic approximation of higher order to the solutions of the semiclassical Schrödinger equation for this system. The adiabatic approximation so obtained exhibits two properties that make it suitable for the studies of intense field molecular dynamics: It is valid for any temporal profile of the field, and improves further as the field intensity increases, as reflected in the weakening of the associated residual nonadiabatic couplings with increasing field strength.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455963
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  • 2
    Electronic Resource
    Electronic Resource
    Radiative transitions induced by short laser pulses in atomic collisions: Nonperturbative study of pulse shape effects (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 256-269 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A time-dependent adiabatic electronic representation is defined by solving the local N-level electronic time-dependent Schrödinger equations at each nuclear configuration of a general N-channel, laser-driven molecular system. These solutions are eigenstates of a time-dependent effective Hamiltonian with respect to which the exact time-evolution of the N-state system is adiabatic. For a two-channel system, the time-dependent adiabatic electronic representation depends on an effective area of the laser pulse and geometrical phases that are also functionals of the laser pulse shape. This adiabatic representation is used in constructing an algorithm for the generation and propagation of wavepackets in a two-channel system irradiated by a short laser pulse. The algorithm is applied to the study of the wavepacket dynamics in the Na–Ar collisional system excited by short laser pulses. The dynamics of the channel populations are analyzed as functions of the shape, duration, and intensity of the laser pulses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462513
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  • 3
    Electronic Resource
    Electronic Resource
    Nonperturbative wave packet dynamics of the photodissociation of H2+ in ultrashort laser pulses (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 5497-5515 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The wave packet dynamics of the photodissociation of H2+ under excitation by laser pulses of short durations at 329.7 nm are studied. The photodissociation process involves essentially two coupled channels, and the detailed mechanism for the formation of fragment kinetic energy spectra is examined by following the evolution of structures in the coupled-channel wave functions in momentum space. These structures appear in the channels' momentum wave functions at P≠0, as the v=0 ground vibrational state is promoted to the dissociative channel then accelerated. The variations of these structures reflect the interplay between local laser-induced transitions and the accelerating–decelerating action of intrinsic molecular forces. The wave packet dynamics are studied for rectangular and Gaussian pulses of varying durations and peak intensities. In addition, two forms of channel couplings were considered corresponding to two different choices of the gauge: the electric-field (EF) gauge, in which the matter–field interaction is of the length form and the radiation-field (RF) gauge, in which it is of the velocity form.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463783
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  • 4
    Electronic Resource
    Electronic Resource
    Description of homoaromaticity in terms of electron distributions (1983)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 105 (1983), S. 5069-5075 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00353a036
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  • 5
    Electronic Resource
    Electronic Resource
    Synthesis and phosphorus-31 and hydrogen NMR characterization of two new chiral ruthenium hydrides containing the trans-1,2-bis((diphenylphosphino)methyl)cyclobutane ligand (TBPC): cis-H2Ru(TBPC)2 and trans-HRuCl(TBPC)2 (1987)
    s.l. : American Chemical Society
    Inorganic chemistry 26 (1987), S. 773-774 
    Details
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ic00252a026
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  • 6
    Electronic Resource
    Electronic Resource
    Time-resolved laser control of vibrational excitations in molecules (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 1528-1539 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We show that, on a short time scale, the dynamics of vibrational excitations in multimode ground-state molecular systems, linearly coupled to a laser field, can be expressed as a simple functional of the laser pulse area. The dependence of the vibrational system's dynamics on a field area leads to simple algebraic equations for this area, in the formulation of the inverse problem associated with the time-resolved control (tracking) of vibrational excitations. The control equation to be solved is quadratic in the area, when the object of the time-resolved control is the total vibrational energy, and linear when the object to be controlled is an average elongation (position tracking), or the average energy of a remotely coupled mode. This yields a control algorithm which requires no iteration and is easy to implement. Numerical tests of the algorithm are performed on the energy and position trackings in simple one-dimensional model systems. An excellent analytical, approximate description of the laser-driven dynamics of these systems is obtained using the concept of Lewis invariant. This analytical description is used as a reference with which the field numerically generated by solving the inverse control problem, using the aforementioned algorithm, can be compared. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468885
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  • 7
    Electronic Resource
    Electronic Resource
    Molecular dichotomy within an intense high-frequency laser field (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 1229-1239 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: It is shown that, under an intense high-frequency laser field, electronic distributions in molecules exhibit a dichotomy effect just as previously found in atoms. The generalization of the formal demonstration of the dichotomy effect as given in M. Gavrila and J. Shertzer, Phys. Rev. A 41, 477 (1990) to many-electron, polyatomic molecules is considered and the validity of the α0−2/3 scaling law of the Floquet eigenvalues, with respect to the field intensity parameter α0 of the HFFT, is discussed. To test the molecular dichotomy effect, numerical calculations are performed using a quantum chemical package (Gaussian 94), modified appropriately to incorporate the cycle-averaged displacements of the nuclear–electron Coulomb potential as found in the HFFT hamiltonian. Results of calculations on the two-electron H2 molecule are presented with an emphasis placed on the character of the total and orbital charge distributions and on trends to be observed in the electronic correlation at high intensities. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480675
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  • 8
    Electronic Resource
    Electronic Resource
    Simultaneous Extraction and Methylation of Acidic Analytes Adsorbed onto Ion Exchange Resins Using Supercritical Carbon Dioxide Containing Methyl Iodide (1995)
    s.l. : American Chemical Society
    Analytical chemistry 67 (1995), S. 945-951 
    Details
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ac00101a023
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  • 9
    Electronic Resource
    Electronic Resource
    Dynamical quenching of field-induced dissociation of H2+ in intense infrared lasers (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 3974-3986 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamics of dissociation of the hydrogen molecular ion H2+ in an intense infrared (IR) field is studied by a series of wave packet simulations. In these simulations, the molecular ion is assumed to be instantly prepared at the initial time by a sudden ionization of the ground-state H2 parent molecule, and a variety of frequency and intensity conditions of the laser field are considered. A new stabilization mechanism, called dynamical dissociation quenching, is found operative in the IR spectral range. In a time-resolved picture, this effect is shown to arise when a proper synchronization between the molecular motions and the laser field oscillations is ensured. In the Floquet, dressed molecule picture, the effect is related to interferences between the Floquet resonances that are excited initially by the nonadiabatic, sudden preparation of the ion. The Floquet analysis of the wave packets in this low frequency regime reveals important intersystem couplings between Floquet blocks, reflecting the highly multiphoton character of the dynamics. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475800
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  • 10
    Electronic Resource
    Electronic Resource
    Dynamical quenching of laser-induced dissociations of heteronuclear diatomic molecules in intense infrared fields (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 4737-4749 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This article explores the influence of permanent dipole moments, i.e., of direct vibrational excitations, on the dynamical dissociation quenching (DDQ) effect, a mechanism for laser-induced vibrational trapping in the infrared (IR) spectral range which was recently demonstrated for the homonuclear H2+ ion, and was shown to result from a proper synchronization of the molecular motions with the oscillations of the laser electric field [see F. Châteauneuf, T. Nguyen-Dang, N. Ouellet, and O. Atabek, J. Chem. Phys. 108, 3974 (1998)]. To this end, the wave packet dynamics of the HD+ and, to a lesser extent, the HCl+ molecular ions are considered in an intense IR laser field of variable frequency. Variations in the absolute phase of the laser electric field, a form of variations in the initial conditions, reveal new signatures of the DDQ effect due to the presence of nonzero permanent dipole moments in these molecules. The added permanent dipole/field interaction terms induce a discrimination between parallel and antiparallel configurations of the aligned molecule with respect to the laser's instantaneous electric field. As a result, molecules that are prepared antiparallel to the field at peak intensity find their dissociation quenched most efficiently, while those that are prepared parallel to the field are strongly dissociative. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478361
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