Molecular dynamics (MD) computer simulations are carried out for scattering of high-energy Xe atoms off liquid squalane, and the results are compared with those of molecular-beam scattering experiments. A crude model for squalane is adopted, describing the hydrocarbon chain molecule as a sphere, and ignoring the role of internal modes. Good overall agreement is found between the results of the simulations and experiment, both for angular distributions and for trends in energy transfer properties. In particular, excellent agreement is obtained for the dependence of the energy transfer on the deflection angle for in-plane scattering. Theory predicts less trapping events than found experimentally, probably due to the crude model adopted for the squalane molecules. The partial success of the model in predicting some properties and not others is discussed. The other main conclusions of the study are (1) The instantaneous local structure of the liquid surface is highly corrugated, giving rise to a broad angular distribution and to extensive out-of-plane scattering. (2) High-energy atoms undergo both a trapping desorption and also direct inelastic scattering, the latter yielding information on liquid structure. (3) The angular distribution of atoms at a selected final velocity is sensitive to the local structure and dynamics of the surface. (4) The direct scattering can be conveniently interpreted in terms of contributions from single, double, and multiple collision events, these being roughly equal in relative weight. Forward scattering at grazing angle is dominated by single collisions, while double and multiple collisions have higher contribution at other directions. The double collision contribution in particular contains structural information. (5) There is a substantial yield per collision for sputtering of the squalane-like soft spheres. These results provide insight into the dynamics of gas–liquid collisions, and indicate the usefulness of beam scattering as a tool for studying liquid structure and dynamics.

No abstract

Simon's exterior-scaling procedure is applied to model systems within the framework of the finite-basis-set approximation. We show that if the basis-set functions are scaled when r )ro, a variational solution is obtained by adding the term , 5(r -ro)[d/drk][lexp( -2iB)] to the Hamiltonian, where k is the logarithmic derivative of the resonance wave function at ro. Two computational methods are proposed. One is an ab initio linear variational iterative procedure, whereas in the second one A, is semiclassically estimated during the iteration procedure and all the variational calculations are carried out for r ro and therefore are exactly 6 independent. An illustrative numerical application is presented.

Up to now tunneling rates in bound systems have been obtained primarily by semiclassical or wave packet calculations. A new accurate quantum time-independent method is presented. Those irregular eigenfunctions of bound systems which diverge asymptotically, but upon complex scaling of coordinates X→X exp(iΘ) become square integrable functions and are associated with complex eigenvalues are found to describe barrier penetration processes. The imaginary part of each of the complex eigenvalues of the complex scaled Hamiltonian contains the tunneling decay rate provided that the Balslev–Combes rotation angle is large enough. The appearance of a critical value Θc as the rotational angle Θ is varied, at which a sharp transition from a real energy spectrum of the bound system to a complex eigenvalue spectrum is an indication of an exponential decay through the potential barrier. Tunneling in multiple barrier problems is important in several areas of physics and chemistry, including isomerization reactions, Josephson junction superconductors, electron tunneling from a 1D metallic lattice under the influence of a uniform electric field (field emission), and tunneling in the EF 1Σg state of molecular hydrogen. Several representative numerical examples are presented.