PHOTOCHEMISTRY OF O-2 ON AG(110) USING PICOSECOND ULTRAVIOLET-LASER PULSES

Surface second-harmonic generation (SHG) was used to study the photoch emical reaction of O-2 with Ag(110) using similar to 6 ps laser pulses . A clean well-ordered Ag(110) surface produces a strong SHG signal at 580 nm. The SHG signal measured in real time during O-2 exposure is s ensitive to submonolayer coverages of O-2 and to the subsequent exposu re of this system to picosecond ultraviolet laser pulses. Upon O-2 ads orption at 130 and 200 K, the signal decreases by more than a factor o f 2 at saturation coverage. Langmuir adsorption kinetics are used to f it the O-2 dosage curves relating the decrease in SHG intensity to the oxygen coverage. Subsequent exposure of the surface dosed at 130 K to 290 nm light of the same pulse width also produces a change in the se cond-harmonic response. Combined with surface SHG temperature programm ed desorption measurements, these results are correlated to the photoc hemical reaction taking place on the surface in which chemisorbed O-2 photodissociates and photodesorbs. The results of the surface photoche mical reaction initiated by picosecond UV pulses are compared to those previously studied using continuous wave radiation and are found to h ave similar overall behavior while possibly showing some new features. (C) 1996 American Vacuum Society.