Quantum study of Eley-Rideal reaction and collision induced desorption of hydrogen atoms on a graphite surface. I, H-chemisorbed case

Collision induced (CI) processes involving hydrogen atoms on a graphite surface are studied quantum mech. within the rigid, flat surface approxn., using a time-dependent wave packet method. The Eley-Rideal (ER) reaction and collision induced desorption (CID) cross sections are obtained with the help of 2 propagations which use different sets of coordinates, a product and a reagent set. Several adsorbate-substrate initial states of the target H atom in the chemisorption well are considered, and CI processes are studied over a wide range of projectile energy. (i) the Eley-Rideal reaction is the major reactive outcome and (ii) CID cross sections do not exceed 4 .ANG.2 and present dynamic thresholds for low values of the target vibrational quantum no. ER cross sections show oscillations at high energies which cannot be reproduced by classical and quasiclassical trajectory calcns. They are related to the vibrational excitation of the reaction products, which is a rather steep decreasing function of the collision energy. This behavior causes a selective population of the low-lying vibrational states and allows the quantization of the product mol. states to manifest itself in a collisional observable. A peak structure in the CID cross section is also obsd. and is assigned to the selective population of metastable states of the transient molecular hydrogen.