A QM/MM model for O(3P) reaction with an alkyl thiolate self-assembled monolayer

Abstract

A QM/MM potential energy surface model is developed for the reaction of O(3P) with a self-assembled monolayer (SAM) of alkyl thiolate chains on Au{111}. The QM part of the model consists of O(3P) and CH3–(CH2)n– surface moieties of a group of the SAM's central alkyl thiolate chains. A model for this QM part is developed by refitting the PM3 semiempirical electronic structure theory to specific reaction parameters (SRPs). In this model, the CH3–CH2– group represents the surface moieties and experimental and high-level ab initio data for the O(3P)+C2H6→OH+C2H5 reaction are used to fit the SRPs. The resulting QM/MM potential energy surface is used in an initial trajectory simulation of O(3P) reaction with the n-hexyl thiolate SAM/Au{111} surface as a function of incident energy and azimuthal angle. The trajectories are restricted to the triplet potential energy surface. The results of this preliminary and incomplete trajectory study are compared with a related recent experimental study of O(3P) with liquid squalane (D.J. Garton, T.K. Minton, M. Alagia, N. Balucani, P. Casavecchio, G.G. Volpi, Faraday Discuss. 108 (1997) 387). A complete trajectory study of the O(3P)+n-hexyl thiolate SAM reaction dynamics, based on this QM/MM model, will be reported later.