Scattering of NO Molecules from Surfaces

Abstract

Surface scattering experiments with atomic or molecular beams yield important information on the dynamics of adsorption, desorption and chemical reactions at solid surfaces. As long as only atoms are involved the measurement of the angular distribution and momentum change of the scattered particles provide sufficient insight in the scattering dynamics. However, when molecules are scattered additional information on the change of internal energy is necessary. Recently the possibility to probe the internal state distribution of molecules with high sensitivity by the use of laser light has been successfully used in a number of surface scattering experiments [1–14]. Applying the laser-induced-fluorescence or the multiphoton-ionization technique, these studies have so far mainly concentrated on the determination of rotational state distributions of molecules scattered or desorbed from solid surfaces. In most cases the state populations of molecules leaving the surfaces can formally be described by a Boltzmann distribution with a rotational temperature Trot. However, the rotational temperature is frequently smaller than the surface temperature, even if the molecules had a very long residence time (≧ 10−4 s) on the surface.