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

Carbon dioxide positive ions and neutral molecules are subject to different charge exchange processes when scattered off clean or potassium-covered Pd(111) surfaces under grazing incidence. The time-of-flight method is a suitable tool to investigate these processes with respect to 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 state and work function on the molecular survival. In particular, potassium increases the dissociation probability whereas switching from CO2+ to CO2 projectiles leads to the opposite effect. Furthermore, in the case of CO2 on Pd(111) + K we found evidence for the formation of negative molecular ions, which are known to play an important role in dissociative chemisorption.