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  • 1
    Electronic Resource
    Electronic Resource
    Long-lived states in atom-molecule collisions (1973)
    s.l. : American Chemical Society
    Accounts of chemical research 6 (1973), S. 138-144 
    Details
    ISSN: 1520-4898
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ar50064a005
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  • 2
    Electronic Resource
    Electronic Resource
    Equilibrium properties of transition-metal ion–argon clusters via simulated annealing (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 7683-7695 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The geometrical structures of M+(Ar)n ions, with n=1–14, have been studied by the minimization of a many-body potential surface with a simulated annealing procedure. The minimization method is justified for finite systems through the use of an information theory approach. It is carried out for eight potential-energy surfaces constructed with two- and three-body terms parametrized from experimental data and ab initio results. The potentials should be representative of clusters of argon atoms with first-row transition-metal monocations of varying size. The calculated geometries for M+=Co+ and V+ possess radial shells with small (ca. 4–8) first-shell coordination number. The inclusion of an ion-induced-dipole–ion-induced-dipole interaction between argon atoms raises the energy and generally lowers the symmetry of the cluster by promoting incomplete shell closure. Rotational constants as well as electric dipole and quadrupole moments are quoted for the Co+(Ar)n and V+(Ar)n predicted structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462369
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  • 3
    Electronic Resource
    Electronic Resource
    Construction of effective Hamiltonians for time-dependent phenomena from variational principles (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 3607-3613 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We develop a variational method for constructing the effective Hamiltonian that best propagates the state of a system, based on the minimization of a temporal error functional. As an illustrative example the procedure is used to derive the effective Hamiltonian in the time-dependent self-consistent-field method. The present variational approach is particularly useful to build the best effective Hamiltonian that is a linear combination of the generators of a Lie algebra. We explicitly consider systems having classical analogs with many degrees of freedom and calculate transition probabilities for a simple semiclassical model of the collinear collision between an atom and a diatomic molecule. We show that our variational approach is more general and accurate than the widely used local harmonic approximation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460811
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Collision time-correlation functions in the semiclassical limit. II. Vibrational–rotational energy transfer in molecule–molecule collisions (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 750-759 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A semiclassical limit of collisional time-correlation functions is applied to energy transfer in collisions between two molecules. The internal degrees of freedom (vibration and rotation) are treated quantum mechanically while the relative motion is described by classical trajectories for fixed molecular orientations. Hence the theory is well-suited to the analysis of energy and angular distributions in collisions governed by general intermolecular potentials, including highly anisotropic short-range forces. Cross sections are given as Fourier transforms of correlation functions of time-evolution operators for the internal degrees of freedom. These operators are determined by action integrals of the intermolecular forces evaluated along the classical trajectories. Correlation functions for coupled harmonic vibrations are obtained using an operator algebra. Rotational correlation functions are calculated by means of an asymptotic expansion appropriate to large transfers of angular momentum. Compact analytical expressions are derived for cross sections in collisions involving symmetric-top, spherically symmetric, and linear molecules. Expressions for average rotational energy transfer, readily obtainable from time-of-flight experiments, are also derived for symmetric top molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452278
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  • 5
    Electronic Resource
    Electronic Resource
    Collisional time-correlation functions in the semiclassical limit. III. Application to vibrational–rotational energy transfer in collisions of Li+ with N2 (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 760-775 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We apply a previously developed treatment of energy tranfer based on collisional time-correlation functions (TCFs) to Li+ scattered from N2 at hyperthermal velocities. Double differential cross sections are calculated using a previously available, realistic potential energy surface for this system. After sucessfully testing the TCF results against independent calculations, we present an in-depth study of vibrational–rotational energy transfer over a wide range of scattering angles (θ=10–175 deg) and collision energies (E=4–17 eV). We also carry out a comprehensive comparison with time-of-flight experiments and explain the observed bimodal structure of energy loss spectra. This has led to a modification of the available translation–vibration coupling potential. The calculations are based on the conditions of slow rotational motion and low vibrational excitation, and involve classical trajectories for relative motions generated at each possible orientation of N2. Cross sections were obtained from interpolations of Tables of more than 60 000 trajectories. Vibrational and rotational motions were described quantum mechanically within a previous treatment based on operator algebras.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452279
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    A generalized intermediate picture of quantal time evolution using operator algebraic methods. Application to translational–vibrational energy transfer in molecular collisions (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 3537-3541 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A method for solving the time-dependent Schrödinger equation in an intermediate picture defined by an effective time-dependent Hamiltonian is discussed. The state function in this intermediate picture is written as a linear combination of time-independent basis functions with time-dependent coefficients. It is shown how to use Lie algebraic methods to build the interaction potential in the intermediate picture and calculate physical observables. The construction of the interaction potential is explicitly discussed in the case of one degree of freedom with a classical coordinate analog. The effective Hamiltonian is obtained by expanding the potential energy function around a reference value of the coordinate. Effective Hamiltonians for He–H2 collisions obtained for equilibrium and average reference values of the vibrational coordinate of H2 are compared and the expansion convergence in the resulting intermediate pictures are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459775
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  • 7
    Electronic Resource
    Electronic Resource
    Calculation of vibrational transition probabilities in molecular collisions: A recursive algebraic procedure (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 924-928 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibrational energy transfer in collinear collisions between diatomic molecules is studied by means of a recursive algebraic approach applicable to several degrees of freedom. Introducing classical relative trajectories the problem is reduced to solving the Schrödinger equation with a time-dependent bilinear Hamiltonian. On using the equations of motion for the creation and annihilation operators, simple recurrence relations for the transition amplitudes are obtained. Transition probabilities between several vibrational states are calculated for N2+O2 to illustrate the advantages of the computational approach for high vibrational quantum numbers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457143
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  • 8
    Electronic Resource
    Electronic Resource
    Vibrational excitation in collisions between two diatomic molecules using an operator algebra (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 5093-5100 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We introduce an operator algebra to study vibrational–translational energy transfer and apply it to collinear collisions between two diatomic molecules. The system is modeled by two linearly driven parametric oscillators with a bilinear time-dependent coupling between them. We describe the time evolution of the linearly driven parametric oscillators accounting for part of the coupling with a sequence of transformations that reduces the coupling at each step, and use perturbation theory to account for the remainder. Results of a basis set expansion are compared with those of the algebraic approach for the collisions N2+O2, N2+CO, and H2+H2. The algebraic approach requires solving a substantially smaller number of coupled differential equations, and gives very good agreement for all systems, for several transitions and relative collision energies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451701
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  • 9
    Electronic Resource
    Electronic Resource
    The linearly driven parametric oscillator: Application to collisional energy transferf a@f ) (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 4926-4936 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The time-evolution operator is explicitly constructed for a general linearly driven parametric quantum oscillator, equivalent to a harmonic oscillator driven by linear plus quadratic potentials. The method is based on an algebra of operators which are bilinear in the position and momentum operators, and form a closed set with respect to commutation. The obtained result requires only integrals over time and the solution of two coupled first order linear differential equations related to the classical equations of motion. The model is used to obtain vibration-translation probabilities in a collinear collision of an atom with a diatomic molecule. Numerical calculations have been performed for systems with several mass combinations and potential parameters. Approximation methods are compared, and criteria are established to determine when it is necessary to go beyond the popular linearly driven harmonic oscillator.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448666
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    Paper (German National Licenses)
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  • 10
    Electronic Resource
    Electronic Resource
    The linearly driven parametric oscillator: Its collisional time-correlation functionf a@f ) (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 4937-4942 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A time-correlation function is explicitly constructed for the linearly driven parametric oscillator. The model is applied to atom–diatomic collinear collisions with a Boltzmann distribution of the initial states of the diatomic molecules. Illustrative numerical calculations have been performed for He–H2 scattering in a semiclassical approximation. The Fourier coefficients of the time-correlation functions can be readily calculated, and provide transition probabilities. A pronounced difference is found between results for the harmonic oscillator and the parametric oscillator models of He+H2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448667
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