Jane Hylton McCreery

A model potential for chemisorption: H2+W(001)

A potential function to describe the interaction of a diatomic molecule with a solid surface is formulated as a modified LEPS potential. The surface is approximated by a rigid background potential, periodic in the plane of the surface. It is assumed that the individual atom–atom and atom–surface potentials are known and can be reasonably approximated by Morse functions. H2+W (001) is presented as an example. One adjustable Sato parameter is introduced and by varying this parameter a wide range of potentials can be generated. The functional form is sufficiently simple so that classical trajectory studies of the reaction dynamics are feasible. Several illustrative trajectories are presented.

Atomic recombination dynamics on solid surfaces: Effect of various potentials

A model potential for gas–solid interactions has been used to investigate the dynamics of recombination of two atoms initially adsorbed on a solid surface. In the spirit of Polanyi’s investigation into the effect of the potential energy surface on the dynamics of gas‐phase reactions, a range of gas–solid potential energy surfaces has been constructed. Classical trajectories have been used to study the dynamics of reactions on those surfaces. It has been found that many of the rules postulated by Polanyi for energy requirements and disposal mechanisms for gas‐phase systems are applicable also to the case of recombination of adsorbed atoms to form a gas‐phase molecule. Previous work assumed a rigid surface providing a static background potential in which the adsorbed atoms moved. An extension of this model is described in which the rigid surface restriction is relaxed and one or more surface atoms are allowed to move interacting with the adsorbed atoms. Using this potential the rigid surface model is shown to be a good approximation for describing many aspects of recombination dynamics.

Atomic recombination dynamics on a solid surface: H2+W(001)

A model potential to describe the interaction of a diatomic molecule with a rigid solid surface has been described previously. Using this interaction potential, a series of classical trajectory calculations have been carried out, designed to simulate the recombination dynamics of two hydrogen atoms initially adsorbed on a tungsten (001) solid surface to form a gas‐phase hydrogen molecule. The vibrational and rotational state distributions of the desorbed hydrogen molecules are discussed in terms of a simple statistical model. The angular and speed distributions for the desorbed atoms and molecules are presented. The angular distributions are found to be substantially noncosine in form and peaked towards the surface normal, in qualitative agreement with experiment.

Dynamics of atom-adsorbed atom collisions: Hydrogen on tungsten

A model potential to describe the interaction of a diatomic molecule with a solid surface has previously been derived and applied to the case of H 2 interacting with a tungsten (001) surface. Using this potential we have computed a series of classical trajectories designed to simulate the collision of a gas-phase hydrogen atom with an adsorbed hydrogen atom. Comparisons are made with the results of recombination studies of two adsorbed atoms and with the collision of an atom with a bare surface.

Recombination dynamics of hydrogen on a tungsten surface

The results of a series of classical trajectory calculations designed to simulate the recombination of two hydrogen atoms adsorbed on tungsten to form a gas phase H2 molecule are reported. (AIP)

Dynamics of adsorption: Model calculations for several interaction potentials

A model potential to describe the interaction of a diatomic molecule with a rigid solid surface has been derived previously. Using this interaction potential, classical trajectory calculations have been carried out to study the dynamics of adsorption on a solid surface. Several forms of the interaction potential were employed so as to observe the effect of different types of potential surfaces on adsorption dynamics, and both H2 and HD were used in these model calculations in order to study the isotope effects on adsorption. Sticking probabilities for the different cases are reported and the validity of the rigid surface model is discussed.

Dynamics of adsorption on covered surfaces

A previous model for the interaction of a diatomic molecule with a solid surface is extended to allow the treatment of three atoms interacting with the solid. The effect of an adsorbed atom on the diatom–solid surface potential is examined. The dynamics of adsorption of a hydrogen molecule in the presence of an adsorbed hydrogen atom is studied. For the potential function used, the dissociative sticking probability of the incident molecule decreases for closer collisions with the adsorbed atom.

Dynamics of adsorption: A model calculation for HD activated adsorption

Abstract We have recently developed a model potential for the interaction of a diatomic molecule with a rigid solid surface. In this note, we report some results of classical trajectory studies designed to simulate the adsorption of a diatomic molecule. Model potentials with different barrier heights are used and a variety of different initial conditions for the incident molecule are studied. In common with gas-phase results, we find that translational energy is most effective in surmounting early barriers and enhancing adsorption.

Gas-solid energy transfer: effect of internal vibrational energy☆

Abstract Classical trajectories were run simulating the collision of a diatomic molecule with a solid surface on a realistic potential energy surface. Previous model potentials have been generalized to include lattice dynamics in the solid surface and, hence, the possibility of gas-solid energy transfer. This energy transfer is examined as a function of the vibrational state of the diatomic molecule and is found to be rather insensitive to added vibrational energy. A means is suggested to utilize this effect to separate vibrationally excited molecules from unexcited ones by adsorption on a surface.

Pattern recognition in chemical dynamics

Abstract We have used pattern recognition methods to predict the outcome of classical trajectory calculations directly from the initial conditions, bypassing the need to integrate the trajectories numerically. Two schemes have been used, a nearest neighbor method (NN) and an adaptive digital learning network (DLN). In each, prediction success greater than 80% is achieved. Both schemes use a suitable training set of known trajectories to teach recognition of initial conditions and prediction of trajectory results. For the present example (two atoms recombining on a solid surface), NN achieves a saving in computer time of a factor of roughly 500 over integrating the trajectories. For DLN this factor is about 100.