Paper SS-TuP4
Radical Reactions with Organic Surfaces

Tuesday, November 11, 2014, 6:30 pm, Room Hall D

Motivated by recent ultra-high-vacuum surface experiments, we have used electronic structure methods, quantum mechanical/molecular mechanical calculations, and molecular dynamics simulations to investigate the structure and reactions of radicals with organic surfaces.

For the first reaction being studied, that of ozone with C60 fullerene, we have characterized stationary points in the potential energy surface for the reactions of O3 with C60 that include both the formation of primary ozonide and subsequent dissociation reactions of this intermediate that lead to C–C bond cleavage. We have also investigated the addition of multiple O3 molecules to the C60 cage to explore potential reaction pathways under the high ozone flux conditions used in recent experiments. The lowest-energy product of the reaction of a single ozone molecule with C60 that results in C–C bond breakage corresponds to an open-cage C60O3 structure that contains ester and ketone moieties at the seam. This open-cage product is of much lower energy than the C60O + O2 products identified in prior work, and it is consistent with IR experimental spectra. Subsequent reaction of the open-cage C60O3 product with a second ozone molecule opens a low-energy reaction pathway that results in cage degradation via the loss of a CO2 molecule. Our calculations also reveal that, while full ozonation of all bonds between hexagons in C60 is unlikely even under high ozone concentration, the addition of a few ozone molecules to the C60 cage is favorable at room temperature.

We have also investigated the reaction of nitrate radicals with functionalized self-assembled monolayer surfaces. Specifically, using quantum mechanical/molecular mechanical calculations, we have calculated vibrational modes of nitrate-SAM products that are consistent with IR experimental spectra. Also, using molecular dynamics simulations, we are able to describe the orientation of the alkanethiol chains that form the surface in order to provide insight into reaction mechanisms under further experimental study.