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  • 1
    Electronic Resource
    Electronic Resource
    Photodissociation of Ar–HCl: An energy-resolved study of the dynamics of total fragmentation into H+Ar+Cl (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2606-2619 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: UV photolysis of Ar–HCl is simulated by means of an exact wave packet treatment in three dimensions. The focus of the work is on the mechanism of indirect dissociation of the hydrogen atom, which leads to total fragmentation of Ar–HCl into H, Ar, and Cl. The results predict for this photodissociation path a probability of about 13% of the photolysis process. The remaining probability would be associated with direct photodissociation of the H fragment. Kinetic-energy distributions of the hydrogen fragments produced by indirect photodissociation are calculated for different excitation energies of Ar–HCl. The distributions reflect a pronounced structure of peaks associated with broad and overlapping resonances of the system. The resonance structure is present in the whole energy range covered by the absorption spectrum. Hydrogen atoms initially populating the resonances can dissociate from the cluster extensively cooled down, after several collisions with Ar and Cl. A mechanism is suggested for the fragmentation process due to indirect photodissociation, which involves successive jumps of the hydrogen to lower-energy resonances, induced by the collisions. A classical collisional model is proposed to rationalize qualitatively the fragmentation dynamics. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479536
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  • 2
    Electronic Resource
    Electronic Resource
    A test of the accuracy of the partially-separable time-dependent self-consistent-field approach (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 8286-8297 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The accuracy of the time-dependent self-consistent-field (TDSCF) approach assuming partial factorization of the total wave packet is tested against an exact treatment, when applied to calculate asymptotic properties. The test is carried out in the framework of a three-dimensional simulation of the Ar–HCl UV photodissociation dynamics. All the partially-separable TDSCF ansatzs possible for this problem are investigated. The quality of the TDSCF results is found to be strongly dependent on the specific partially-separable ansatzs applied. In general, the TDSCF predictions are in very good (even quantitative) agreement with the exact ones for magnitudes associated with direct photodissociation dynamics, and are qualitative in the case of indirect photodissociation. The deviation of the TDSCF results from the exact dynamics is interpreted in terms of an error operator defined as the difference between the exact and the TDSCF Hamiltonians. The analysis of this operator also explains the different accuracy of the partially-separable ansatzs investigated. Based on this analysis, a simple procedure is suggested to estimate the relative average quality of the different TDSCF ansatzs. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480172
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  • 3
    Electronic Resource
    Electronic Resource
    A hybrid classical/quantum approach to cluster fragmentation dynamics: Application to the vibrational predissociation of He2Cl2 (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 1989-1996 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new hybrid classical/quantum method is proposed and applied to investigate the vibrational predissociation (VP) dynamics of the He2Cl2 complex. The full dimensionality of the system (assuming zero total angular momentum) is included in the method. The VP process of He2Cl2 is dominated by a sequential mechanism of dissociation of the two van der Waals bonds. The hybrid approach describes the first weak bond fragmentation classically, and the second one quantum mechanically. The rotational distribution of the Cl2 fragment is calculated both with the hybrid method and with a fully classical trajectory simulation, and compared with the experimental distribution. The hybrid distribution is found to agree very well with the experimental one, and to involve a substantial improvement with respect to the classical result. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475578
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  • 4
    Electronic Resource
    Electronic Resource
    An energy-resolved study of the partial fragmentation dynamics of Ar–HCl into H+Ar–Cl after ultraviolet photodissociation (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 4983-4993 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The UV photolysis of Ar–HCl is simulated by an exact wave packet calculation. Partial fragmentation of the cluster into H and Ar–Cl fragments is studied by projecting out the asymptotic wave packet onto the product states, at several excitation energies in the range of the Ar–HCl absorption spectrum. The partial fragmentation pathway is found to dominate the photolysis process at very low excitation energies, and to be intense also at high energies. At medium excitation energies the other competing fragmentation pathway, namely total fragmentation into H, Ar, and Cl, dominates almost completely the photodissociation dynamics. The relative intensity of the two fragmentation pathways depends on the extent to which the hydrogen is initially blocked by Ar and Cl. The Ar–Cl radicals are produced with high rotational and low vibrational excitation at most of the Ar–HCl energies studied. The internal energy distributions of Ar–Cl show remarkable differences in shape depending on the regions of the absorption spectrum which are excited. This effect can be exploited to control both the efficiency of Ar–Cl generation and the internal excitation of the radical prepared, by changing the excitation energy of the parent cluster. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481053
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  • 5
    Electronic Resource
    Electronic Resource
    On the importance of an accurate representation of the initial state of the system in classical dynamics simulations (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 8302-8311 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A definition of a quantum-type phase-space distribution is proposed in order to represent the initial state of the system in a classical dynamics simulation. The central idea is to define an initial quantum phase-space state of the system as the direct product of the coordinate and momentum representations of the quantum initial state. The phase-space distribution is then obtained as the square modulus of this phase-space state. The resulting phase-space distribution closely resembles the quantum nature of the system initial state. The initial conditions are sampled with the distribution, using a grid technique in phase space. With this type of sampling the distribution of initial conditions reproduces more faithfully the shape of the original phase-space distribution. The method is applied to generate initial conditions describing the three-dimensional state of the Ar–HCl cluster prepared by ultraviolet excitation. The photodissociation dynamics is simulated by classical trajectories, and the results are compared with those of a wave packet calculation. The classical and quantum descriptions are found in good agreement for those dynamical events less subject to quantum effects. The classical result fails to reproduce the quantum mechanical one for the more strongly quantum features of the dynamics. The properties and applicability of the phase-space distribution and the sampling technique proposed are discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481435
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  • 6
    Electronic Resource
    Electronic Resource
    Study of the total and partial fragmentation dynamics of Ar–HCl after uv photodissociation (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 5755-5766 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The uv photolysis of the Ar–HCl cluster is studied applying an exact time-dependent wave packet method in three dimensions, assuming zero-total angular momentum. The photodissociation process is found to occur via two different fragmentation mechanisms, depending on the initial excitation energy of the cluster. One mechanism leads to total dissociation of the complex, producing three fragments, Ar–HCl+hν→H+Ar+Cl. The fragmentation dynamics in this case is governed by resonance states at relatively low energies of the cluster, in which the H atom collides a number of times with Ar and Cl before dissociating. Manifestations of these collisions are found in the final kinetic energy distribution of the photofragments, which is redshifted in the case of the H fragment, and blueshifted in the Ar and Cl cases. The second type of mechanism consists of a fast and direct photodissociation of the hydrogen, leading to a partial fragmentation of Ar–HCl into hot H fragments and bound Ar–Cl radical molecules. This mechanism dominates at higher energies, which are those mostly populated by the wave packet initially prepared in the present calculations. The experimental implications of the results are discussed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475986
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  • 7
    Electronic Resource
    Electronic Resource
    Quantum-mechanical study of the I2–Ne vibrational predissociation dynamics: A three-dimensional time-dependent self-consistent-field approach (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 1047-1055 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A three-dimensional time-dependent self-consistent-field (TDSCF) approach is proposed to study the vibrational predissociation of the I2(B)–Ne van der Waals (vdW) complex. Jacobian coordinates are used within the assumption of zero-total angular momentum. In the method the total wave function is factorized such that the bending mode of the system is explicitly separated, while the coupling between the remaining two degrees of freedom is treated exactly. The decay dynamics of several resonances corresponding to different initial vibrational states of I2 is investigated through long-time wave packet propagations. Calculated resonance lifetimes are compared to experimental data and found to be in quantitative agreement with them. The results show that predissociation of the complex is mainly governed by the coupling between the I2 and the vdW stretching vibrations, whereas the bending mode has a rather weak effect on the dynamics. The good quality of the TDSCF description of this long-time dynamical process is due to the adaptation of the decoupling approximations applied in the method to the physical situation of the system. The validity of the approach is discussed in the light of the results. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470830
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  • 8
    Electronic Resource
    Electronic Resource
    Quasiclassical dynamics of the I2–Ne2 vibrational predissociation: A comparison with experiment (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 8405-8412 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibrational predissociation dynamics of the I2(B,v)–Ne2 complex is investigated for several vibrational levels of I2, using a quasiclassical trajectory approach. The time evolution of the population of nascent I2 fragments is calculated. A model is proposed which reproduces the results of the classical trajectories, and allows to obtain the lifetimes associated with the dissociation of the two van der Waals (vdW) bonds. The classical lifetimes are higher in general than the experimental ones of Zewail and co-workers [J. Chem. Phys. 97, 8048 (1992)]. The classical method appears to overestimate mechanisms of energy redistribution between the modes, which slow down the dissociation of the cluster. However, the behavior of the lifetimes with the initial iodine vibrational excitation is in very good agreement with experiment. A sequential path of fragmentation of the two weak bonds via direct predissociation is found to dominate, producing I2(B,v–2)+2Ne fragments. Although with smaller probability, alternative dissociation paths are observed involving statistical mechanisms of internal energy redistribution. In these paths, the energy initially transferred by the iodine heats the vdW modes without breaking the complex. Further energy transfer produces either simultaneous or sequential dissociation of the two weak bonds in a rather evaporative way, populating the v–2 and v–3 exit channels. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471590
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  • 9
    Electronic Resource
    Electronic Resource
    Three-dimensional quantum wave packet study of the Ar–HCl photodissociation: A comparison between time-dependent self-consistent-field and exact treatments (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 3463-3473 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The time-dependent self-consistent-field (TDSCF) approximation is used to study the photodissociation of the Ar–HCl cluster in a three-dimensional framework. The results are compared with numerically exact quantum calculations, and the properties and accuracy of the TDSCF approach are evaluated on this basis. The TDSCF approximation is used in Jacobi coordinates, and the total wave function is factorized into a wave packet for two coordinates associated with the H atom, and a wave packet for a single coordinate that describes the relative motion of the heavy particles. Quantitative agreement between the TDSCF and the exact results is found for most quantities calculated. The calculations show that photodissociation, and in particular the departure of the H atom is predominantly a direct process, but an appreciable amount of wave packet amplitude moving in excited state resonances is also found. This amplitude seems significantly larger than obtained in recent calculations by Schröder et al. [J. Chem. Phys. 100, 7239 (1994); Chem. Phys. Lett. 235, 316 (1995)]. The validity and computational efficiency of the TDSCF approach for realistic systems of this type is discussed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470230
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  • 10
    Electronic Resource
    Electronic Resource
    A reduced-dimensionality quantum model which incorporates the full-dimensional energy of the system: Application to the vibrational predissociation of Cl2–Ne2 (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 2146-2156 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A reduced-dimensionality quantum model is proposed which incorporates the zero-point energy of the neglected modes in a systematic, natural way. In this model the reduced-dimensionality Hamiltonian is obtained by averaging the exact Hamiltonian over the dependence of the full-dimensional initial state of the neglected modes. The reduced Hamiltonian conserves all the terms of the full Hamiltonian, providing a more flexible description of the couplings between the modes considered explicitly in the model. The model is applied to simulate the vibrational predissociation dynamics of Cl2–Ne2, considering the three stretching modes of the complex. The results are compared to experimental data and to previous calculations using a reduced-dimensionality quantum model and a full-dimensional quantum–classical approach. The Cl2–Ne2 resonance lifetimes obtained agree only qualitatively with the experimental and previously calculated ones. By contrast, the present model predicts more correctly than previous calculations the behavior of the Cl2 fragment vibrational distributions observed experimentally. The applicability of the model is discussed and further refinements are suggested. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1385153
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