This presentation will highlight out recent work on energetic gas-surface interactions that lead to outcomes involving collisional energy transfer, isotope dependent embedding and enrichment in ice, and activated reactions. These studies utilize a unique combination of supersonic and hypersonic beam scattering done in conjunction, for reaction studies, with in situ scanning tunneling microscopy. Illustrative experiments will examine the scattering of molecular oxygen from graphite, where we show that final angular and velocity distributions can be quantitatively modelled now using chemical dynamics simulations. Increasing complexity in such interactions will be illustrated by our recent work involving the penetration and energetic embedding of atoms and molecules into ice. Energetic ballistic embedding is a general new scattering channel where incident species can be trapped under conditions dependent upon surmounting momentum and energy constraints to achieve embedding into the sub-surface selvedge region. Featured today will be a new method for isotope enrichment involving the embedding of atoms into ice which exhibits excellent single-pass enrichment as demonstrated for selected isotopes of Xe. Here we generated Xe atomic beams of controlled velocities, relatively narrow velocity distributions, and with all of the entrained isotopes having identical velocities arising from the seeded supersonic molecular beam expansion. Heavier isotope becomes preferentially absorbed, i.e., embedded, in the ice matrix. These findings will have impact on the composition of trapped gases in both terrestrial and astrophysical settings. The final topic to be covered extends to multi-scale spatially-resolved interface reactivity, where in situ STM is being used to monitor spatio-temporal correlations in interfacial reactivity. Time-lapse visualization of reacting interfaces is allowing us to probe the reactivity of specific sites at complex interfaces and how the presence of a reacted site or local region influences the subsequent reaction probability at proximal sites. This approach can also be used to probe the relative importance of adiabatic vs. non-adiabatic interactions in interfacial reactions. Examples will be taken from studies of silicon, graphite oxidation, and molecular chemisorption. The aforementioned topics have been chosen to illustrate, and honor, themes that we have explored with our longtime colleague Bill Hase.

Energetic gas-surface interactions leading to energy transfer, isotope dependent embedding and enrichment, and activated reactions

ACS Spring Meeting 2021

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