Thermal and Low-Energy Electron-Driven Chemistry of Biacetyl on Ag(111)

The thermal and electron-induced chemistry of biacetyl (CH 3 COCOCH 3 ) on Ag(111) has been studied using temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy, and ultraviolet photoelectron spectroscopy. No thermal decomposition of biacetyl occurs, confirming that Ag(111) is inert with respect to the breaking of C−C, C O, and C−H bonds. There are five molecular biacetyl desorption peaks in TPD 180, 178, 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 biacetyl 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 biacetyl may be directed were explored by irradiating 1 ML of biacetyl with 50 eV electrons. During irradiation, CO, CH 3, ketene (H 2 C C O), and C 2 H 6 desorb. After irradiation, five new post-irradiation TPD peaks appear. These are identified as H 2 at 210 K, CH 4 at 235 and 315 K, H 2 C C O at 240 K, and reaction-limited CH 3 COCOCH 3 at 440 K. XPS shows C (a) and O (a) remain on the surface after heating to 700 K.