Study of the Hydrogen Channel Mechanism in the Dis- sociation of H2 S on Au(111)

PABLO LUSTEMBERG, PAULA NATALIA ABUFAGER ,MARIA LUZ MARTIARENA, ALEJANDRA ELISA MARTıNEZ AND HERIBERTO FABIO BUSNENGO

Italia

Conferencia; 25 European Conference on Surface Science; 2009

The interest in the adsorption dynamics of methanethiol (HSR with R=CH3 ) and the formation  of self-assembled monolayers (SAMs) on metal surfaces has been steadily growing during the  last two decades [1-2]. We found the energy difference between reactives and products of the  H-SCH3 dissociation on Au(111) to be quite similar to the global energetics of the of H-SH  dissociation on Au(111) [3]. Therefore, we believe that the simplest sulfur containing molecule HSH ) might be used as a model system to clarify the reaction mechanism. The so-called  hydrogen channel is a mechanism that involves two HSH molecules and the formation and  desorption of an H2 molecule. The energetic of this reaction has been investigated [4-5],  however no details of the process has been given (i.e. confguration of the transition states, etc.).  Additionally, it has been pointed that the hydrogen channel might become relevant at high  coverages and below the desorption temperature of the molecular state because two adsorbed  molecules close to each other are required for this mechanism to take place. In view of the  above, we propose various possible reaction pathways at different coverages and analyze their  activation energy barrier using a combination of Nudged Elastic Band (NEB) [6-7] and Adaptive  NEB (ANEBA) [8] methods based on the Density Functional Theory. Our results indicate that 1,23 eV is the minimum activation energy barrier for the hydrogen channel  mechanism, which is at least 0,2 eV higher than the corresponding value in the case of the unimolecularmechanism [3]. Therefore this mechanism does not improve the H-SH dissociation on Au(111).[1] J. Love, L. A. Estroff, J. Kriebel, R. Nuzzo, and G. Whitesides, Chem. Rev. 2005, 105, 1103. [2] A. Ulman, Chem. Rev. 1996, 96, 1533. [3] P.N. Abufager, P.G. Lustemberg, C. Crespos, H.F. Busnengo, Langmuir 2008, 24, 14022. [4] H. Sellers Surf. Sci. 1993, 294, 99. [5] J. Gottschalack, B. Hammer, J. Chem. Phys. 2002, 116, 748. [6] G.Henkelman, B.P. Uberuaga, and H. J´nsson, J. Chem. Phys. 2000,113, 9901. [7] G. Henkelman and H. J´nsson J. Chem. Phys. 2000,113, 9978. [8] P. Maragakis, et. al., J. Chem. Phys. 2002, 117, 4651.