Photochemistry of O2 on Ag(110) using picosecond ultraviolet laser pulses

Abstract

Surface second-harmonic generation (SHG) was used to study the photochemical reaction of O2 with Ag(110) using ∼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 O2 exposure is sensitive to submonolayer coverages of O2 and to the subsequent exposure of this system to picosecond ultraviolet laser pulses. Upon O2 adsorption at 130 and 200 K, the signal decreases by more than a factor of 2 at saturation coverage. Langmuir adsorption kinetics are used to fit the O2 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 second-harmonic response. Combined with surface SHG temperature programmed desorption measurements, these results are correlated to the photochemical reaction taking place on the surface in which chemisorbed O2 photodissociates and photodesorbs. The results of the surface photochemical reaction initiated by picosecond UV pulses are compared to those previously studied using continuous wave radiation and are found to have similar overall behavior while possibly showing some new features.