PHOTON-DRIVEN CHEMISTRY OF BIACETYL ON AG(111)

The photon-driven chemistry of biacetyl (CH3COCOCH3) on Ag(111) has be en studied using temperature-programmed desorption, Auger electron spe ctroscopy, and time-of-flight mass spectrometry. Irradiation of both m onolayer and multilayer biacetyl with 193 nm photons results in the pr ompt ejection of CH3 radicals that exhibit bimodal translational tempe ratures of 2700 +/- 100 and 290 +/- 20 K. Irradiation of multilayer bi acetyl with 193 nm also leads to ejection of CO with translational tem peratures of 1170 +/- 40 and 140 +/- 10 K, ketene (CH2CO) with transla tional temperatures of 1000 +/- 60 K, and acetyl-containing fragments with translational temperatures of 320 +/- 20 K. Indicative of the eje ction of all reaction products from the surface during irradiation, po stirradiation TPD shows loss of parent only, and C-(a) and O-(a) are a bsent from the surface after irradiation and subsequent heating to 700 K. The cross section for total loss of 1 ML biacetyl is 2.0 +/- 0.3 x 10(-21) cm(+2) at 193 nm. Studies using 248 nm radiation, as well as radiation from a Hg are lamp, were also undertaken.