Gas-Surface Scattering Dynamics of CO2, NO2, and O3 in Collisions with Model Organic Surfaces

High-energy (70 kJ/mol) molecular beams of CO2, NO2, and O-3 were scattered from long-chain methyl (CH3-), hydroxyl (OH-), and perfluoro (CF3(CF2)(8)-, or F) omega-functionalized alkanethiol self-assembled monolayers (SAMs) on gold to study the dynamics of energy exchange and thermal accommodation of atmospherically important triatomic molecules on model organic surfaces. Overall, the extent of energy transfer in gas collisions with all of the surfaces studied was substantial. Specifically, the triatomics scatter from each surface only after dissipating greater than 80% of their incident energy. Furthermore, although the OH-SAM is a more rigid surface, the extent of energy transfer and accommodation of these molecules to the CH3- and OH-SAMs were approximately the same. The similar scattering dynamics are likely due to significant gas-surface attractive forces between the triatomics and the OH- terminal groups, which compensate for the rigidity of this monolayer. In contrast to the OH- and CH3-SAMs, the dominant pathway in collisions of the gases with the F-SAM was impulsive scattering. The portion of molecules that accommodated (<40%) to the F-SAM was about half of the amount that accommodated (similar to 70%) to the CH3- and OH-SAMs. Although differences in the surface properties had a significant effect on the dynamics, variances in the chemical and physical properties of the three gases, CO2, NO2, and O-3, were found to have little effect on the extent of energy transfer and accommodation for collisions with any one surface.