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  • 1
    Electronic Resource
    Electronic Resource
    Quantum-mechanical calculations of the dissociation of H3 Rydberg states (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 4283-4292 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present three-dimensional, time-dependent quantum-mechanical calculations of the dynamics of the dissociation of H3 Rydberg states at total energies up to 6 eV. The method used in this work employs a Chebychev propagator in time, and computes the kinetic-energy operators in the discrete variable representation. We calculate the total dissociation cross section, as well as partial vibrational and rotational cross sections, and compare our results to previous two-dimensional calculations and to experiment. The results display clear three-dimensional effects, and indicate the importance of including both sheets of the H3 ground potential-energy surface in the dynamics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462822
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  • 2
    Electronic Resource
    Electronic Resource
    An exact coupled-channel study of the transition state spectroscopy of the collinear H+H2 reaction (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 6401-6408 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present an exact coupled-channels method for calculating free-bound transition dipole amplitudes in reactive chemical systems. The method employs a log-derivative propagator in hyperspherical coordinates and the artificial channel method to calculate the desired integrals implicitly. We apply this method to a study of the transition state spectroscopy of the collinear H+H2 reaction, analyzing in detail the effect of the reactive Feshbach resonances on the spectra. A statistical analysis of the spectral intensity fluctuations shows that at low collision energies the intensity distribution is poorly fit by the Porter–Thomas distribution. As the collision energy increases, the fit becomes very good, indicating strongly coupled degrees of freedom. These results indicate the importance of considering the preparation of the initial state when performing statistical analyses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456306
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  • 3
    Electronic Resource
    Electronic Resource
    Coherent control of bimolecular chemical reactions (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 1126-1131 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We show how the method of coherent control can be applied to control product yield in bimolecular chemical reactions. First, a laser pulse prepares a coherent superposition of two bound levels of an electronically excited state of the reactants. Then, after a variable delay, a second laser pulse photodissociates the system to the ground state continuum. By varying the detuning of the excitation pulse and the delay between the two pulses, we show that significant control of the product ratio can be achieved. As a first application of the method we demonstrate, with exact quantum-mechanical calculations, the control of the collinear H+H2 and D+H2 reactions. The pulses and delays used in these calculations are on the order of picoseconds, a range of time scales well within that achievable with conventional laser systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458174
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  • 4
    Electronic Resource
    Electronic Resource
    Derivation of femtosecond pump–probe dissociation transients from frequency resolved data (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 5499-5507 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a theoretical synthesis of Zewail's femtosecond transition state (FTS) experiments. The FTS transients are obtained by convoluting the continuous wave, bound–free, and free–free frequency-resolved spectra with the pump and probe laser pulses. We accomplish this by deriving a simple semiclassical expression for the free–free (as well as the bound–free) matrix elements and regularizing the divergent integrals occurring in the free–free integrals, by subtracting a δ-function singularity. This method allows us to write the FTS transient signal as a coherent superposition of a "molecular'' term and an "atomic'' term, which shows clearly the effects of the interaction between the on-resonance and off-resonance transients observed in Zewail's experiments. Our method, which achieves essentially the same accuracy as the purely numerical wave-packet propagation techniques, is much more efficient. It enables an easy exploration of all possible pump–probe configurations and clearly confirms the fact that quantum mechanics does not allow a unique definition of a "bond-breaking'' time. In fact, we show that the observed transients are a strong function of the laser preparation and probing. In addition, we demonstrate that the assumption that the initial wave packet is localized after absorption of a 50–100 fs pulse is wrong, and that the classical approximation that there exists a one-to-one correspondence between the probe frequency and the internuclear distance of the photofragments is inaccurate. We show that the parameters obtained by the use of these classical approximations for the free–free spectrum lead to the extraction of the wrong potential parameters which, in turn, leads to a discrepancy between the calculated and measured bound–free absorption spectrum. This discrepancy does not exist if the potential parameters are extracted quantum mechanically.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460485
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  • 5
    Electronic Resource
    Electronic Resource
    Optical control of molecular dynamics: Molecular cannons, reflectrons, and wave-packet focusers (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 6562-6578 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We consider the control of molecular dynamics using tailored light fields, based on a phase space theory of control [Y. J. Yan et al., J. Phys. Chem. 97, 2320 (1993)]. This theory enables us to calculate, in the weak field (one-photon) limit, the globally optimal light field that produces the best overlap for a given phase space target. We present as an illustrative example the use of quantum control to overcome the natural tendency of quantum wave packets to delocalize on excited state potential energy curves. Three cases are studied: (i) a "molecular cannon'' in which we focus an outgoing continuum wave packet of I2 in both position and momentum, (ii) a "reflectron'' in which we focus an incoming bound wave packet of I2, and (iii) the focusing of a bound wave packet of Na2 at a turning point on the excited state potential using multiple light pulses to create a localized wave packet with zero momentum. For each case, we compute the globally optimal light field and also how well the wave packet produced by this light field achieves the desired target. These globally optimal fields are quite simple and robust. While our theory provides the globally optimal light field in the linear, weak field regime, experiment can in reality only provide a restricted universe of possible light fields. We therefore also consider the control of molecular quantum dynamics using light fields restricted to a parametrized functional form which spans a set of fields that can be experimentally realized. We fit the globally optimal electric field with a functional form consisting of a superposition of subpulses with variable parameters of amplitude, center time, center frequency, temporal width, relative phase, and linear and quadratic chirp. The best fit light fields produce excellent quantum control and are within the range of experimental possibility. We discuss relevant experiments such as ultrafast spectroscopy and ultrafast electron and x-ray diffraction which can in principle detect these focused wave packets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465848
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  • 6
    Electronic Resource
    Electronic Resource
    Controlling the Future of Matter (1995)
    s.l. : American Chemical Society
    Accounts of chemical research 28 (1995), S. 133-140 
    Details
    ISSN: 1520-4898
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ar00051a006
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  • 7
    Electronic Resource
    Electronic Resource
    Spectral quantization of transition state dynamics for the three-dimensional H+H2 reaction (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 1725-1729 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Applying a spectral quantization method, we find the positions and widths of 32 transition state resonances in the three-dimensional reaction H+H2 with J=0. The assignment of many of the resonances appears to follow asymmetric stretch and bend progressions for a linear triatomic molecule.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467728
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  • 8
    Electronic Resource
    Electronic Resource
    Quantum control of multidimensional systems: Implementation within the time-dependent Hartree approximation (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 173-182 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The exact formulation of quantum control is now well known and sufficiently general to describe multidimensional quantum systems. The implementation of this formalism relies on the solution of the time-dependent Schrödinger equation (TDSE) of the system under study, and thus far has been limited for computational reasons to simple quantum systems of very small dimensionality. To study quantum control in larger systems, such as polyatomic molecules and condensed phases, we explore an implementation of the control formalism in which the TDSE is solved approximately using the time-dependent Hartree (TDH) approximation. We demonstrate formally that the TDH approximation greatly simplifies the implementation of control in the weak response regime for multidimensional systems. We also present numerical examples to show that the TDH approximation for the weak response case is sufficiently accurate to predict the laser fields that best drive a quantum system to a desired goal at a desired time, in systems containing more than one degree of freedom, by considering a two-dimensional quantum system and comparing the optimal fields obtained by solving the TDSE exactly to those obtained using the TDH approximation. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470887
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  • 9
    Electronic Resource
    Electronic Resource
    Quantum Control of Molecular Dynamics: The Strong Response Regime (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 13736-13747 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100037a022
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  • 10
    Electronic Resource
    Electronic Resource
    Detection and control of molecular quantum dynamics (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 14949-14958 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100041a008
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