Reaction Dynamics At Surfaces, A-Molecule-At-A-Time

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This research proposes to exploit an opportunity which has arisen in recent years to obtain detailed understanding of the way in which simple chemical reactions take place at surfaces. The opportunity stems from the confluence of three fields of contemporary research: Scanning Tunneling Microscopy (STM) (Nobel Prize in Physics, 1986) experimental Reaction Dynamics (Nobel Prize in Chemistry, 1986) and the development of Computer Models revealing the molecular dynamics in complex reactive encounters (Nobel Prize in Chemistry, 2013). STM, allows the experimenter to obtain images of single molecules at surfaces. Reaction Dynamics (a field pioneered by the applicant with many others) is the experimental study of the molecular motions that give rise to chemical reaction. Computer modeling reveals the complex atomic and molecular motions that transform reagents into products. A combination of these three fields offers, for the first time, the opportunity to see individual reagent molecules at surfaces, follow their activation by heat, light or electrons, and correlate their initial and final geometries. "Theoretical chemistry provides us with the whole drama," said the Chair of the Chemistry Nobel Selection Committee in announcing the Chemistry award for molecular modeling, this week.** The opportunity to map the molecular motions in the course of surface reactions, a-molecule-at-a-time, is the subject of the present proposal. This laboratory is well placed for studies of this type, since it combines experiment with computer-based theory. Specifically (1) it is equipped, exceptionally, with four Ultra-High Vacuum STM's for studies of reactions at the well-characterized surfaces of semi-conductors and metals, and (2) it has recently introduced and demonstrated (in five published papers from the present granting period) an ab initio model (the 'Impulsive Two-State', I2S, model) that serves as a guide to the sequence of molecular motions responsible for converting reagent, whose geometry at the surface is observed by STM, into products, whose geometry is observed by the same means.** The purpose of the proposed work is to provide understanding at the molecular level of an event central to chemistry, as also to life, namely the ability of chemical reactions to convert one substance into another--breaking old bonds and forming new. The fundamental question of Reaction Dynamics is how reagents approach, how they collide, and how they separate. One experimental approach proposed here (first demonstrated by us for a simple chemical reaction followed by STM, in the present reporting period) is to position and align a pair of reagents at the surface, and then trigger 'Surface Aligned Reaction' (SAR) by excitation of one of the molecular pair. Other experimental approaches that form a part of this Proposal are studies of Low-Temperature Surface Reaction by charge-transfer from the surface, and Dependence of Reaction Dynamics on Mode of Reagent Excitation by comparing vibrational with electronic excitation.** These experiments and their accompanying theories have an evident practical purpose, as demonstrated in results reported here from the current period of research, since progress in fabricating nano-structures will depend on our knowledge of, and ability to control, the location and binding of reaction products at surfaces. A powerful means to pattern surfaces, 'Molecular-Scale Imprinting', shown here to be applicable to semi-conductors and (for the first time) also to metals, is described in this submission. NSERC Discovery Grants by fostering far-reaching basic science offer the best possible hope for subsequent transformative applications.