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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 6831-6837 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We investigate the photofragmentation of HOD in the first absorption band. Full three-dimensional quantum mechanical calculations on an ab initio excited state potential are presented. They are based on the IOS approximation for the rotational (bending) degree of freedom. The remaining two-dimensional problem is treated exactly using hyperspherical (polar) coordinates. HOD absorption spectra are compared with recently published results for H2O and D2O. Dissociation of the vibrational ground state favors the production of OD fragments, in agreement with physical intuition. The final vibrational distributions for OH and OD are relatively broad indicating strong final state interaction. They are broader for OD but inverted for OH products. Cross sections for the dissociation of vibrationally excited stretching states are also compared with those for H2O and a strong isotope effect is found. The branching ratio depends significantly on the initial vibrational state of the parent molecule. The quantum mechanical results are compared with simple classical calculations and generally very good agreement is found. Within the classical limit all data are readily understandable.
    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. 129-148 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report a detailed theortical study of the photodissociation of H2O and D2O in the first absorption band (λ∼165 nm). The calculations are three dimensional and purely quantum mechanical. They include an ab initio potential energy surface for the A˜ state and a calculated SCF dipole moment function for the X˜→A˜ transition. The dynamical calculations are performed within the infinite-order-sudden approximation for the rotational degree of freedom of OH and the LHL approximation for the masses. The resulting vibrational–translational motion is then treated exactly in two dimensions using hyperspherical coordinates. This study does not include any adjustable parameters. The thermally averaged total absorption spectra for H2O and D2O agree perfectly with the experimental spectra. Even finer details such as the progression of "vibrational'' structures are well reproduced. They are not induced by any selective absorption but can be explained on the basis of the A˜ state potential energy surface and details of the dissociation dynamics. Vibrational excitation of the OH and OD products is significantly wavelength dependent. The distribution of the three lowest vibrational states at 157 nm is in good accord with recent LIF measurements. Particular attention is paid to the sensitivity of the final results with respect to the coordinate dependence of the transition dipole function, the parent nuclear wave function and the excited state potential energy surface.
    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 87 (1987), S. 4310-4314 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The C˜→A˜ emission spectra for H2O and D2O are measured and calculated. The theoretical model is based on an exact treatment of the dissociation dynamics of the A˜ state using a calculated potential energy surface. Agreement with the measurements is excellent. The spectra extend from λ∼380 nm up to λ∼600 nm with maxima around 425 (H2O) and 440 nm (D2O).
    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 116 (2002), S. 4762-4764 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We discuss an excitation scheme, where the interaction of two ultrashort laser pulses prepares an ensemble of ionized molecules with an oscillating average bond length. By adjusting the delay-time between the pulses it is possible to vary the oscillation period continuously within the subpicosecond regime. Possible applications in producing electron beams, modulated on a femtosecond time scale, are outlined. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 8132-8138 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present transients obtained by femtosecond time-resolved spectroscopy on I2 encapsulated in well-defined cages of the crystalline microporous SiO2 modification deca-dodecasil 3R. After pump excitation into the electronic B-state, collision-induced predissociation is observed followed by recombination into A/A′ and X states, where the molecules undergo vibrational relaxation. To explain the complex time-behavior of the transient signals, molecular dynamics simulations are performed which account for the nonadiabatic transitions in I2 and the adsorbate-framework interactions. The theoretical study shows that the total signal contains contributions from four optical transitions which are influenced by predissociation and vibrational relaxation processes. A pronounced dependence of the transient signals on the probe-laser wavelength is determined by the position of the resonance window for the optical transition. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 6585-6591 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We use three-dimensional classical molecular dynamics to simulate femtosecond time-resolved experiments on the caging dynamics of I2 in rare gas environments [Wan et al., J. Chem. Phys. 106, 4353 (1997)]. The calculated pump–probe signals are in excellent agreement with experiment. Prominent oscillatory structures as observed in the pump–probe signals are interpreted in terms of caustics which appear in the classical bound state dynamics of the caged molecules. The results confirm conclusions based on a simple statistical model which treats the collisions as random perturbations involving hard sphere scattering. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 4844-4849 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Absorption spectra for the collinear (nonreactive) H+H2→H#3 →H+H2 are calculated quantum mechanically, using the Siegbahn–Liu–Truhlar–Horowitz (SLTH) ab initio potential and a model H@B|3 surface as the ground and excited H3 surface, respectively. They are compared to classical spectra previously computed by Mayne, Poirier, and Polanyi using the same potential energy surfaces [J. Chem. Phys. 80, 4025 (1984)]. The spectra are calculated at several collision energies and for both H+H2 (v=0) and H+H2 (v=1). The quantal and classical spectra are shown to agree with respect to basic features and trends. Nevertheless, the two sets of spectra differ considerably in their overall appearance because of some purely quantum aspects of the H+H2 system.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 3609-3614 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A bound-to-free transition initiated by femtosecond excitation of diatomic molecules results in photofragments with a distribution of kinetic energies. A measurement of the kinetic-energy distribution yields the modulus squared of the asymptotic momentum-space wave packet prepared in the laser excitation process. On the other hand, the coordinate-space density of the wave packet entering the interaction-free region can be determined from pump–probe integrated fluorescence spectroscopy. We provide several numerical examples to show that this information can be used to determine the phase of the asymptotic wave packet so that this particular quantum-mechanical wave function can be characterized completely. To achieve this aim we use an iteration scheme (Gerchberg–Saxton algorithm) which does not require any further information about the system or the laser pulses. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 5770-5775 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We calculate pump–probe signals obtained from femtosecond excitation of I2 molecules. It is shown that, depending on the parameters of the pump laser-pulse, the signals can exhibit a regular oscillatory behavior although the vibrational wave packet which is produced in the pump process, is delocalized over the entire classically allowed region. The respective structures can be related to temporal variations of an enhanced probability density which, in turn, are related to the underlying classical motion. We further demonstrate that the use of time-resolved photoelectron spectroscopy allows for a characterization of the structures which appear in the time-dependent wave function. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Computer Physics Communications 63 (1991), S. 228-242 
    ISSN: 0010-4655
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Computer Science , Physics
    Type of Medium: Electronic Resource
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