THERMAL AND LOW-ENERGY ELECTRON-DRIVEN CHEMISTRY OF BIACETYL ON AG(111)

The thermal and electron-induced chemistry of biacetyl (CH3COCOCH3) on Ag(111) has been studied using temperature-programmed desorption (TPD ), X-ray photoelectron spectroscopy, and ultraviolet photoelectron spe ctroscopy. No thermal decomposition of biacetyl occurs, confirming tha t Ag(111) is inert with respect to the breaking of C-C, C=O, and C-H b onds. There are five molecular biacetyl desorption peaks in TPD-180, 1 78, 174, 188, and 215 K. The peak at 180 K is attributed to monolayer adsorption, and its saturation peak area is used to scale other TPD bi acetyl peaks. The peak at 188 K is assigned to multilayers and that at 215 K to desorption from defect sites. The peaks at 174 and 188 K are discussed in terms of coverage dependent reorientation and bilayers. Nonthermal excitation pathways by which the surface chemistry of biace tyl may be directed were explored by irradiating 1 ML of biacetyl with 50 eV electrons. During irradiation, CO, CH3, ketene (H2C=C=O), and C 2H6 desorb. After irradiation, five new post-irradiation TPD peaks app ear. These are identified as H-2 at 210 K, CH4 at 235 and 315 K, H2C=C =O at 240 K, and reaction-limited CH3COCOCH3 at 440 K. XPS shows C-(a) and O-(a) remain on the surface after heating to 700 K.