A new collision dynamics study on the H2 formation after atom recombination on a tungsten surface at TS=500K has been undertaken. The semiclassical collisional method [1] has been used according to which the classical Hamilton’s equations of motion of the two hydrogen atoms are solved in an effective Hamiltonian obtained by averaging the interaction potential over the total phonon wave function. Therefore, the dynamical coupling between the classical degrees of freedom of the H/H2 species and the quantized surface phonons is taken into account. The potential energy surface assumed in the dynamics was that obtained by Forni et al. [2] within the tight-binding model.
Firstly, the Eley-Rideal recombination mechanism has been investigated at impact energies of the H atom impinging the tungsten surface in the range 0.005-3eV.
The reaction probability together with the energy partitioning between the different degrees of freedom of the formed H2 molecules have been calculated. The adsorption site effect on the reaction dynamics was also investigated in detail.
Preliminary results on the H2 formation via the Langmuir-Hinshelwood collisional mechanism will be also presented and discussed.
The calculated collisional data, in particular the probabilities for recombination and for adsorption/desorption processes, may have an impact on the chemistry of the H atoms at the reactor walls of fusion devices [3].
[1] M. Rutigliano, M. Cacciatore, G.D. Billing, Chem.Phys. Lett. 340 (2001)13
[2] A. Forni, M.C. Desjonquères, D. Spanjaard and G.F. Tantardini, Surface Science 274 (1992)161
[3] R.A. Causey, Journal of Nuclear Materials 300 (2002) 91
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