Quantum State-Resolved CO2Collisions at the Gas−Liquid Interface:  Surface Temperature-Dependent Scattering Dynamics.

Energy transfer dynamics at the gas−liquid interface are investigated as a function of surface temperature both by experimental studies of CO2perfluorinated polyether (PFPE) and by molecular dynamics simulations of CO2fluorinated self-assembled monolayers (F-SAMs). Using a normal incident molecular beam, the experimental studies probe scattered CO2internal-state and translational distributions with high resolution infrared spectroscopy. At low incident energies Einc1.6(1) kcal/mol, CO2J-state populations and transverse Doppler velocity distributions are characteristic of the surface temperature (TrotTtransTS) over the range from 232 to 323 K. In contrast, the rotational and translational distributions at high incident energies Einc10.6(8) kcal/mol show evidence for both trapping-desorption (TD) and impulsive scattering (IS) events. Specifically, the populations are surprisingly well-characterized by a sum of Boltzmann distributions where the two components include one (TD) that equilibrates with the surface (TTDTS) and a second (IS) that is much hotter than the surface temperature (TISTS). Support for the superthermal, yet Boltzmann, nature of the IS channel is provided by molecular dynamics (MD) simulations of CO2F-SAMs Einc10.6 kcal/mol, which reveal two-temperature distributions, sticking probabilities, and angular distributions in near quantitative agreement with the experimental PFPE results. Finally, experiments as a function of surface temperature reveal an increase in both sticking probability and rotational/translational temperature of the IS component. Such a trend is consistent with increased surface roughness at higher surface temperature, which increases the overall probability of trapping, yet preferentially leads to impulsive scattering of more highly internally excited CO2from the surface. [ABSTRACT FROM AUTHOR]