The o(2) oxidation reaction of graphite was studied by preparing Cs promoters in two different states: Cs adsorbed on a surface [Cs(ad)] and Cs trapped underneath a surface carbon plane [Cs(tr)]. Reactive ion scattering spectrometry (RIS) and, scanning tunneling microscopy (STM) were used to identify the reaction intermediates and to measure the spatial range of the Cs promoter effect. Cs(ad) promotes the oxidation reaction in a localized region through formation of CsO and CsO2 intermediates. On the other hand, Cs(tr) promotes the reaction over a long range, such that a large number (similar to10(3)) of O-2 molecules are chemisorbed at a graphite surface and etch away the surface carbons.