Formation of surface-bound acyl groups by reaction of acyl halides on ge(100)-2x1.
We have investigated the reaction of a series of acyl halides, including acetyl chloride, acetyl bromide, acetyl-d3 chloride, benzoyl chloride, and pivaloyl chloride, on Ge(100)-2x1 with multiple internal reflection infrared (MIR-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT). Infrared spectra following saturation exposures of acetyl chloride and acetyl bromide to Ge(100)-2x1 at 310 K are nearly identical, both exhibiting strong nu(C=O) stretching peaks near 1685 cm-1 and no vibrational modes in the nu(Ge-H) region. These data provide strong evidence for the presence of a surface-bound acetyl group on Ge(100)-2x1, which results from a C-X dissociation reaction (where X=Cl, Br). For acetyl chloride, DFT calculations predict that the barrier to C-Cl dissociation is only 1 kcal/mol above a chlorine-bound precursor state and is considerably smaller than barriers leading to the [2+2] C=O cycloaddition and alpha-CH dissociation products. In addition to the C-X dissociation product, both infrared and photoelectron results point to the presence of a second structure for acetyl halides where the oxygen of the surface-bound acetyl group donates charge to a nearby surface atom. This interaction is not observed for benzoyl chloride and pivaloyl chloride.
Filler
Michael A
MA
Department of Chemical Engineering, Stanford University, Stanford, California 94305, USA.
Keung
Albert J
AJ
Porter
David W
DW
Bent
Stacey F
SF
D000215:Acylation; D003460:Crystallization; D005857:Germanium / Q000737:chemistry*; D006843:Hydrocarbons, Chlorinated / Q000737:chemistry*; D015394:Molecular Structure; D013055:Spectrophotometry, Infrared; D013057:Spectrum Analysis; D013499:Surface Properties; D014965:X-Rays
D006843:Hydrocarbons, Chlorinated; D005857:Germanium