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  • 1
    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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  • 2
    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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  • 3
    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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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    LOCATIONAL FACTORS IN THE DECLINING INDUSTRIAL COMPETITIVE ADVANTAGE OF THE NEW YORK URBAN REGION (1986)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of regional science 26 (1986), S. 0 
    Details
    ISSN: 1467-9787
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geography , Economics
    Notes: This paper investigates the locational factors that contributed to the decline of the New York urban region's industries during 1972-1975. Based on the static concept of a specialization index, a dynamic comparative advantage index is constructed. A model is then formulated to test the hypothesis that regional competitive advantage (vis-à-vis the nation) is a function of relative disparities in the change of these locational factors. Regression results show that the region's competitive advantage is influenced positively by the differential rate of change in market size, by the differential profit rate before tax, and negatively by the differential rate of change in unit labor cost and in unit energy cost. The differential tax rate does not seem to affect the region's competitive advantage. Nevertheless, a progressive corporate income tax structure tends to neutralize the beneficial effects of the economies of agglomeration and the urban attraction of the region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1467-9787.1986.tb00335.x
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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Higher order adiabatic separation of strongly coupled systems. I. Two-body systems and dressed hydrogen atom (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 7224-7231 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The phase corrected adiabatic separation method proposed recently by Marechal [J. Chem. Phys. 83, 247 (1985)] is reexamined. We have been able to show that a state independent differential equation exists, which governs the phase coupling function f of this method, if f further satisfies a set of constraints, Eqs. (7) of the present paper. The method is illustrated by its application to three simple, exactly soluble two-body systems: the free hydrogen atom, the linearly forced hydrogen atom, and the system of two harmonically coupled oscillators. We show that for these systems, the present method, which employs an adiabatic separation procedure, after phase correcting the Hamiltonian, leads to exact results, suggesting its utility for more general problem, involving nonseparable potentials. A nonseparable system of particular interest is the dressed hydrogen atom, which is a representative of all dressed systems, molecular or atomic, with respect to radiative couplings. The method of phase corrected adiabatic separation is shown to give, for field frequencies lying below an IR threshold, a better representation for the exact eigenstates of this dressed systems, as ensuing residual couplings are estimated to be of second order in the original radiative coupling constant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451359
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  • 8
    Electronic Resource
    Electronic Resource
    Molecular dynamics in intense fields. III. Nonadiabatic effects (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 2840-2850 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: It is shown that coupled equations for multiphoton processes can be written with either momentum transition moments or dipole transition moments. In perturbation (low field intensity) theories, nonadiabatic corrections are necessary to make the adiabatic momentum electronic transition probabilities nonzero and equivalent to electronic dipole transition probabilities in infrared transitions. For strong fields, nonadiabatic interactions can become important due to multiphoton resonances, and both approaches necessitate full coupled equations. In the case of electronic excitations, adiabatic, nuclear dipole transition probabilities become nonzero and equivalent to nuclear momentum transitions probabilities only after nonadiabatic corrections are included. These corrections should become important at strong fields for electronic states coupled nonadiabatically. It is shown further using a representation which introduces field modified electronic functions and electronic potentials that unusual field effects will occur at photon frequencies in resonance with adiabatic electronic potential energy separations at pseudo (avoided) crossings. Thus, in such cases, electronic energy gaps are increased by the field and nonadiabatic couplings at these avoided crossings are reduced by the field. Strong resonant fields should therefore quench nonadiabatic couplings at avoided crossings, rendering nonadiabatic reactions more adiabatic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449234
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  • 9
    Electronic Resource
    Electronic Resource
    Nonadiabatic interactions of anharmonically coupled oscillators (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 5019-5027 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The validity of the adiabatic approximation applied to systems of two coupled oscillators–typically represented by the Henon–Heiles' Hamiltonian–is examined. Through explicit analytical estimates of nonadiabatic couplings, it is shown that the adiabatic approximation is appropriate in all cases, except for the case of 1:1 Fermi resonance between the two oscillators. In this case, nonadiabatic couplings are found to be important already at an excitation energy of about two quanta, i.e., at much lower energies than Ec, the critical energy for the classically observed quasiperiodic–chaotic transition. Nonadiabatic interactions are dominantly horizontal at these energies (E〈Ec), however, indicating some regularity in the energy spectrum at low excitation, despite the early breakdown of the adiabatic separation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449768
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  • 10
    Electronic Resource
    Electronic Resource
    Dynamical quenching of laser-induced dissociations of diatomic molecules in intense infrared fields: Effects of molecular rotations and misalignments (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 2197-2207 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamical dissociation quenching (DDQ) effect is a new mechanism for laser-induced vibrational trapping of molecules in the infrared (IR) spectral range. Previously demonstrated for one-dimensional, prealigned diatomic molecules [see F. Châteauneuf, T. Nguyen-Dang, N. Ouellet, and O. Atabek, J. Chem. Phys. 108, 3974 (1998)], the effect was shown to result from a proper synchronization of the molecular motions with the oscillations of the laser electric field. The present paper explores the influence of rotations and misalignment of the molecular system on the DDQ effect. To this end, the two-dimensional (radial and angular) wave-packet dynamics of the H2+ and HD+ molecular ions are considered in an intense IR laser field starting from two types of initial angular distributions: The first type of distributions is appropriate for a field-free, pure angular momentum eigenstate and denotes typically an initially nonaligned, nonoriented molecule. The second type denotes a more or less well aligned and/or oriented initial condition, and is described by an angular width Δ which is considered a parameter in terms of which the efficiency of the DDQ effect are monitored. We demonstrate that the DDQ effect remains efficient whenever a proper compromise is achieved between angular localization and angular-momentum (action) minimization. From the detailed analysis of the time-resolved dynamics, a time scale is also estimated for the molecule-field synchronization process which underlies the DDQ effect. An ultrafast laser-induced rotational-electronic energy transfer is found to compete with the DDQ effect, in the case the initial rotational state denotes an almost perfect alignment and/or orientation situation. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1328378
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