Effects of thermal roughening on the angular distributions of trapping and scattering in gas-liquid collisions

Atomic beam scattering experiments are used to investigate collisions of 71 kJ/mol of argon atoms with perfluorinated polyethers (PFPE) over a wide range of liquid temperatures (T-liq) and incident and exit angles. At temperatures ranging from 280 to 359 K, argon atom energy transfer and trapping at the PFPE interface increase steadily with more normal approach directions. Trapping also grows with T-liq for all approach and exit directions we measured. The fractional change of trapping with T-liq is 2-5 x 10(-3) K-1, rising weakly with more grazing impact angles. in contrast, the inelastic scattering flux decreases with increasing T-liq, at forward scattering angles and increases for backward deflections. These results are consistent with a surface of protruding hard sphere-like CFx groups that becomes more corrugated at higher temperatures, promoting multiple collisions of incoming atoms at all impact angles.