SCATTERING OF CARBON-DIOXIDE MOLECULES FROM PD(111) SURFACES

Carbon dioxide positive ions and neutral molecules are subject to diff erent charge exchange processes when scattered off clean or potassium- covered Pd(111) surfaces under grazing incidence. The time-of-flight m ethod is a suitable tool to investigate these processes with respect t o dissociation and different charge state formation. Using projectiles with primary energies of 250 up to 1500 eV we found not only a strong energy dependence but also a sizeable influence of initial charge sta te and work function on the molecular survival. In particular, potassi um increases the dissociation probability whereas switching from CO2to CO2 projectiles leads to the opposite effect. Furthermore, in the c ase of CO2 on Pd(111) + K we found evidence for the formation of negat ive molecular ions, which are known to play an important role in disso ciative chemisorption.