Filler Michael A, Keung Albert J, Porter David W, Bent Stacey F
Department of Chemical Engineering, Stanford University, Stanford, California 94305, USA.
J Phys Chem B. 2006 Mar 9;110(9):4115-24. doi: 10.1021/jp055685+.
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.
我们利用多重内反射红外光谱（MIR-IR）、X射线光电子能谱（XPS）和密度泛函理论（DFT），研究了一系列酰卤，包括乙酰氯、乙酰溴、乙酰-d3氯、苯甲酰氯和新戊酰氯，与Ge(100)-2x1表面的反应。在310 K下，乙酰氯和乙酰溴饱和暴露于Ge(100)-2x1表面后的红外光谱几乎相同，均在1685 cm-1附近出现强的ν(C=O)伸缩峰，且在ν(Ge-H)区域没有振动模式。这些数据为Ge(100)-2x1表面存在表面结合的乙酰基提供了有力证据，这是由C-X解离反应（其中X = Cl、Br）导致的。对于乙酰氯，DFT计算预测C-Cl解离的势垒仅比氯结合的前驱体状态高1 kcal/mol，且远小于导致[2+2] C=O环加成和α-CH解离产物的势垒。除了C-X解离产物外，红外和光电子结果均表明酰卤存在第二种结构，即表面结合的乙酰基的氧向附近表面原子提供电荷。对于苯甲酰氯和新戊酰氯，未观察到这种相互作用。
