TIME-OF-FLIGHT INVESTIGATIONS OF O2 SCATTERED FROM PT(111)

A nozzle beam of molecular oxygen was scattered from clean and oxygen-covered Pt(111) surfaces and velocity distributions of the scattered molecules were investigated by time-of-flight (TOF) measurements. From the clean surface at a surface temperature of T(s) = 900 K mainly direct quasi-elastic scattering is observed whereas from the oxygen-covered surface (p(2 x 2) layer as confirmed by LEED) at T(s) = 300 K the TOF distribution is composed of two parts: besides some directly scattered molecules a relatively high number of molecules with a Maxwellian distribution according to T(s) = 300 K appears. These thermalized molecules are attributed to a trapping-desorption channel. Our results provide new and rather direct experimental proof for interpretations of angular distributions already known from literature.