Coadsorbate effects in surface photochemistry: NO and O2 on Pt(111)

Photon-induced desorption (PID) and electron energy loss spectroscopy (EELS) applied to the system NO/O2/Pt(111) yield information on coadsorbate effects in surface photochemistry. A new NO species (denoted γNO) is observed in EELS [νγN−O=236 meV, ν(Pt−γNO)=49 meV], and is found to have a highly enhanced PID cross section compared to that of NO in the top sites of the clean surface [σγNO(O2)(333 nm)=(1.1±0.1)×10−18 cm2]. Photodesorption of O2 is enhanced and photodissociation of O2 is inhibited in the presence of NO resulting in the suppression of NO2 production upon irradiation of NO/O2/Pt(111), in contrast to the photoinduced formation of CO2 from CO/O2/Pt(111). The wavelength dependences of NO and O2 PID cross sections demonstrate that they are independent processes. The final product states created in photoinduced processes with O2 are strongly influenced by coadsorbates.