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  • 1
    Electronic Resource
    Electronic Resource
    The dissociative chemisorption dynamics of N2 on catalytic metal surfaces: A quantum-mechanical tunneling mechanism (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 3346-3355 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A tunneling mechanism is suggested for explaining the dissociative chemisorption of nitrogen molecules on metal surfaces. The time-dependent Schrödinger equation was numerically solved for the transition dynamics from the N2–metal to the N–metal potential-energy surfaces for two degrees of freedom. The dynamics was found to be sensitive to the topology at the crossing region between the two nonadiabatic potential-energy surfaces (PES). The resulting rapid increase of the dissociation probability (S0) with incident kinetic energy, its saturation at high energies and vibrational enhancement are in good agreement with recent experiments. A substantial isotope effect is predicted by the calculations. Recombinative desorption experiments of 14N2 and 15N2 from Re(0001) are in excellent agreement with the tunneling model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456666
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Bi- and unimolecular resonances of the collinear reaction F+DBr(arrow-right-and-left)FDBr(arrow-right-and-left)FD+Br (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 6191-6199 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reaction probability function P(ν'←ν||E) of the bimolecular collinear reaction F+DBr(ν)→FD(ν')+Br shows sharp resonance peaks at certain collision energies Ebi. On the other hand, the unimolecular dissociation FDBr*(ν1ν3)→F+DBr(ν), FD+Br(ν) exhibits long-lived behavior for particular resonance wave functions Ψν1ν3 at energies Euni. Good numerical agreement is found in a comparison of bi- and unimolecular resonance energies and lifetimes by two complementary methods: (i) S-matrix propagation in hyperspherical coordinates for the bimolecular reaction; (ii) the diagonally corrected vibrational adiabatic hyperspherical (DIVAH) method to determine unimolecular resonances, coupled with the fast Hankel transform (FHT) method to propagate them in time. The agreement found suggests a correlation between bi- and unimolecular resonances by the reaction mechanism F+DBr(ν)(arrow-right-and-left)FDBr*(ν1ν3)(arrow-right-and-left)FD(ν')+Br, where the unimolecular resonance states Ψν1ν3 serve as traps or doorway states, blocking or catalyzing the bimolecular reaction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454750
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Inelastic He scattering from a xenon overlayer: Dynamical diffraction effects (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 7556-7563 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A model study is presented which describes the interaction of a gas with a crystalline surface. Both the surface and gas are treated quantum mechanically using a type of mean field approximation for the coupling of the translating particles to the surface. By varying the angle of incidence of the incoming particle, a large diffraction effect is observed for a narrow range of angles. Significant differences between the static and thermal features of the gas–surface scattering are observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456189
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Cross sections for He scattering from surface imperfections: Vacancies and CO adsorbates on Pt(111) (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 3722-3731 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Total cross sections for He scattering from isolated imperfections on surfaces are calculated using the Sudden approximation, and in some cases also by a numerically exact, time-dependent quantum-mechanical wave packet method. Systems studied include: CO adsorbates on Pt(111); mono-, di-, and trivacancies on Pt(111). The main results are: (1) the incidence angle and energy dependence of the cross section for He/[Pt(111)+CO] are very sensitive to the CO distance from the Pt plane. Interactions with the adsorbate image have little effect on the cross section. (2) The cross sections for clusters of vacancies are given within 10% or better, by the geometric sum of the monovacancy cross sections, the latter being treated as circles centered at each monovacancy. (3) The dependence of the cross section on the energy is sufficiently sensitive to distinguish between the "electron density hole'' and "electron density hump'' models for vacancies and vacancy clusters. (4) The Sudden approximation compares well with the exact quantum-mechanical results at typical experimental energies, when the incidence angle is not too far from the normal. These results indicate that experimental measurements of He scattering cross sections as a function of energy and incidence angle, combined with Sudden or wave packet scattering calculations, can provide detailed information on surface defects and their interactions with gas-phase atoms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454712
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  • 5
    Electronic Resource
    Electronic Resource
    Exact time-dependent quantum mechanical dissociation dynamics of I2He: Comparison of exact time-dependent quantum calculation with the quantum time-dependent self-consistent field (TDSCF) approximation (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 2760-2765 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibrational predissociation dynamics of a collinear model of the I2(v)He cluster is studied by numerically exact time-dependent quantum mechanics, and by the time-dependent self-consistent field (TDSCF) approximation. The time evolution for the initial excitation levels v=5, 11, 22 is explored. Excellent agreement is found between the TDSCF and the exact evolution of the wave packet; in particular the approximation reproduces well the dephasing events in the dynamics, and the measurable predissociation lifetimes. The results are very encouraging as to the applicability of quantum TDSCF as a quantitative tool in the study of van der Waals predissociation dynamics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453063
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  • 6
    Electronic Resource
    Electronic Resource
    Validity of time-dependent self-consistent-field (TDSCF) approximations for unimolecular dynamics: A test for photodissociation of the Xe–HI cluster (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 6484-6490 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation dynamics of a collinear model of the van der Waals cluster Xe–HI is used as a testing ground for time-dependent self-consistent field (TDSCF) approximations. In this study, the quantum-mechanical TDSCF and a combined classical/quantal TDSCF (in which the light atom is treated quantum mechanically, the heavy atoms are treated classically) are compared to numerically exact wave packet calculations. Very good agreement is found between the TDSCF approximations and the exact result over the entire subpicosecond time duration of the process. In particular, all the properties related to the quantal degree of freedom in the combined quantal/classical TDSCF method reproduce almost perfectly the exact results. However, the classical mode in the hybrid approximation is somewhat less well described due to insufficient representation of energy transfer between the modes. The conclusions are very promising as to the applicability of TDSCF methods, in particular the hybrid quantal/classical scheme to more complex systems in which only a few degrees of freedom can be treated quantum mechanically.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458965
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  • 7
    Electronic Resource
    Electronic Resource
    A theoretical study of electron–hole pair formation due to the collision of an atom with a solid surface (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 6890-6899 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electronic excitation in a semiconductor induced by the collision of energetic atoms with the solid surface is investigated theoretically. The modeling has been performed for a one-dimensional independent-electron system where the solid is described by a chain of 10–20 atoms. The time evolution of the nuclei (i.e., colliding atom and chain atoms) has been described by classical mechanics while quantum mechanical description has been used for the electronic dynamics. The two systems (i.e., the atoms and the electron) were coupled to each other and the equations of motion were solved self-consistently. Energy dissipation from the chain to the rest of the solid was included via the GLE approach. This study establishes the relationship between the probability of electron–hole formation and various parameters of the system such as collider translational energy, magnitude of the band gap, and existence of impurities in the solid. In addition, two excitation mechanisms were examined, electronic excitation due to a direct coupling between the electron and the colliding atom and an indirect mechanism due to electron–phonon coupling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458922
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  • 8
    Electronic Resource
    Electronic Resource
    Lifetimes of local and hyperspherical vibrational resonances of ABA molecules (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 2626-2638 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The complete spectrum of vibrationally excited ABA* molecular resonance lifetimes is evaluated using the simple Rosen–Thiele–Wilson model of coupled Morse oscillators. Two complementary methods are used: First, unimolecular dissociative resonance wave functions are propagated in time by the Fourier method, where the initial wave functions are obtained as an approximation by linear combinations of symmetry-adapted products of Morse functions. Second, bimolecular reaction S matrices are propagated along the hyperspherical radius of the system giving the diagonalized lifetime matrix, which is analyzed for resonance lifetimes and energies. The resulting uni- and bimolecular resonance energies agree within ±0.002 eV and the lifetimes within ±30%. Uni- and bimolecular assignments of gerade (+) and ungerade (−) ABA* symmetries agree perfectly. On the average, the unimolecular decay times decrease as the resonance energies increase from the ABA*→A+BA to about 3/4 of the A+B+A dissociation threshold; even more highly excited resonances tend to be slightly more stabilized. Superimposed on this overall nonmonotonous energy dependence is a strong, 1–2 orders of magnitude variation of lifetimes, indicating substantial mode selectivity for the decay of individual resonances, irrespective of the excitation energy. The mode selectivity is investigated for hyperspherical mode resonances with lobes extending across the potential valleys, in contrast with local mode resonances with frontier lobes pointing towards the valleys. On the average, hyperspherical mode resonances decay at a slower rate than local mode resonances. This conclusion agrees with our previous analysis of low energy ABA* resonances, and with Hose and Taylor's analysis of the Hénon–Heiles system. However, these correlations are also violated by several important exceptions: the ABA* system has many slowly, but also a few rapidly, decaying hyperspherical resonances.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452754
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  • 9
    Electronic Resource
    Electronic Resource
    Atom scattering from isolated adsorbates on surfaces: Rainbows, diffraction interferences, and trapping resonances (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 7209-7220 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The scattering of He atoms from a CO molecule adsorbed on a Pt surface is studied theoretically by methods that include: (1) Numerically exact solutions of the time-dependent Schrödinger equation for the scattered wavepacket; (2) The sudden approximation; (3) Classical trajectories. The methods are used to obtain detailed insight into the collision dynamics, and to predict and understand interesting features in the angular intensity distribution of the scattered atoms. The analysis and interpretation of the exact quantum results is facilitated by calculations of the probability current density of the scattered particles. Some of the main results are: (i) The angular intensity distribution exhibits nonspecular maxima of two types: Several of the peaks are rainbow effects induced by the adsorbate, while others (at angles nearer to the specular) are Fraunhofer diffraction interferences. Both types of peaks contain useful, largely complementary, information on adsorbate geometry and on the He/adsorbate interaction. (ii) The angular intensity distribution is quantitatively sensitive to the adsorbate distance from the surface, suggesting possible determination of that distance from experimental data. (iii) The corrugation due to the adsorbate leads to scattering resonances associated with temporary trapping of the scattered atom at the defect site. This is a new effect of potential importance for experimental studies of atom/defect interactions. The results obtained here suggest that He scattering from isolated adsorbates exhibits distinct, substantial effects, measurement of which should yield very useful data on the adsorbates and on their interactions with gas-phase atoms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454373
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    Paper (German National Licenses)
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  • 10
    Electronic Resource
    Electronic Resource
    Dynamics of hyperspherical and local mode resonance decay studied by time dependent wave packet propagation (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 993-1004 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Time dependent wave packet propagation of resonance states of ABA molecules is used to demonstrate the correlation between the directionality of the lobes of the wave functions and mode selectivity of the unimolecular decay. This correlation was inferred by Hose and Taylor. The molecule is modeled by the Thiele–Wilson coupled Morse oscillators. A near-degenerate pair of resonances with extreme motions is studied in detail: The local "bond'' mode with lobes pointing towards the exit valleys of the potential decays about 30 times faster than the hyperspherical "restricted precession'' mode with dominant lobe on the potential ridge. This is in close analogy to mode selectivity in the Hénon–Heiles system. The wave function propagation technique also yields detailed insight into the dissociation mechanism. Out of several choices, only a single lobe penetrates into the exit valley. For the local mode resonance vibrational predissociation starts out primarily from extended vibrationally excited diatomic configurations, A↔B(ν*=1)⋅ ⋅ ⋅A→AB(ν'=0)+A. However, the hyperspherical mode resonance prefers compressed diatomic geometry just before dissociation, AB(ν*=3)⋅ ⋅ ⋅A→AB(ν'=0)+A. The results imply some general criteria for mode selective unimolecular chemical reactions, as well as a successful numerical test of the preparation of resonance wave functions and their propagation by the Fourier method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449426
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    Paper (German National Licenses)
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