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

A QM/MM potential energy surface model is developed for the reaction of O(P -3) with a self-assembled monolayer (SAM) of alkyl thiolate chains on Au{1 1 1}. The QM part of the model consists of O(P-3) and CH3-(CH2)(n)- surface moieties of a group of the SAM's central alkyl thiolate chains. A model fo r this QM part is developed by refitting the PM3 semiempirical electronic s tructure theory to specific reaction parameters (SRPs). In this model, the CH3-CH2- group represents the surface moieties and experimental and high-le vel ab initio data for the O(P-3) + C2H6 --> OH + C2H5 reaction are used to fit the SRPs. The resulting QM/MM potential energy surface is used in an i nitial trajectory simulation of O(3P) reaction with the n-hexyl thiolate SA M/Au(III) surface as a function of incident energy and azimuthal angle. The trajectories are restricted to the triplet potential energy surface, The r esults of this preliminary and incomplete trajectory study are compared wit h a related recent experimental study of O(P-3) with liquid squalane (D.J. Garton, T.K. Minton, M. Alagia, N. Balucani, P. Casavecchio, G,G. Volpi, Fa raday Discuss. 108 (1997) 387). A complete trajectory study of the O(P-3) n-hexyl thiolate SAM reaction dynamics, based on this QM/MM model, will be reported later. (C) 2000 Elsevier Science B.V. All rights reserved.