Department of Chemistry, National Cheng Kung University, 1, Ta Hsueh Road, Tainan, Taiwan.
J Chem Phys. 2011 Aug 14;135(6):064706. doi: 10.1063/1.3624348.
Temperature-programmed reaction/desorption, mass spectrometry, reflection-absorption infrared spectroscopy, x-ray photoelectron spectroscopy, and density functional theory calculations have been employed to explore the reaction and bonding structure of 1,2-C(2)H(4)Br(2) on Cu(100). Both the trans and gauche conformers are found to dissociate by breaking the C-Br bonds on clean Cu(100) at 115 K, forming C(2)H(4) and Br atoms. Theoretical investigations for the possible paths of 1,2-C(2)H(4)Br(2) → C(2)H(4) + 2Br on Cu(100) suggest that the barriers of the trans and gauche molecules are in the ranges of 0-4.2 and 0-6.5 kcal/mol, respectively. The C-Br scission temperature of C(2)H(4)Br(2) is much lower than that (~170 K) of C(2)H(5)Br on Cu(100). Adsorbed Br atoms can decrease the dissociation rate of the 1,2-C(2)H(4)Br(2) molecules impinging the surface. The 1,2-C(2)H(4)Br(2) molecules adsorbed in the first monolayer are structurally distorted. Both the trans and gauche molecules exist in the second monolayer, but with no preferential adsorption orientation. However, the trans molecule is the predominant species in the third or higher layer formed at 115 K. The layer structure is not thermally stable. Upon heating the surface to 150 K, the orientation of the trans 1,2-C(2)H(4)Br(2) molecules in the layer changes, leading to the rotation of the BrCCBr skeletal plane toward the surface normal on average and the considerable growth of the CH(2) scissoring peak. On oxygen-precovered Cu(100), decomposition of 1,2-C(2)H(4)Br(2) to form C(2)H(4) is hampered and no oxygenated hydrocarbons are formed. The presence of the oxygen atoms also increases the adsorption energy of the second-layer molecules.
采用程序升温反应/解吸、质谱、反射吸收红外光谱、X 射线光电子能谱和密度泛函理论计算研究了 1,2-C(2)H(4)Br(2)在 Cu(100)上的反应和键合结构。在 115 K 下，无论是顺式还是 gauche 构象，在清洁的 Cu(100)表面，1,2-C(2)H(4)Br(2)通过断裂 C-Br 键均会解离，生成 C(2)H(4)和 Br 原子。关于 1,2-C(2)H(4)Br(2) → C(2)H(4) + 2Br 在 Cu(100)上可能的途径的理论研究表明，trans 和 gauche 分子的势垒分别在 0-4.2 和 0-6.5 kcal/mol 的范围内。C(2)H(4)Br(2)的 C-Br 断裂温度远低于 C(2)H(5)Br 在 Cu(100)上的温度(~170 K)。吸附的 Br 原子可以降低撞击表面的 1,2-C(2)H(4)Br(2)分子的解离速率。在第一层中吸附的 1,2-C(2)H(4)Br(2)分子结构发生扭曲。trans 和 gauche 分子均存在于第二层中，但没有优先的吸附取向。然而，在 115 K 形成的第三层或更高层中，trans 分子是主要物种。层结构不稳定。当加热表面至 150 K 时，层中 trans 1,2-C(2)H(4)Br(2)分子的取向发生变化，导致 BrCCBr 骨架平面平均朝向表面法线旋转，CH(2)的剪式峰显著增大。在预覆盖有氧气的 Cu(100)上，1,2-C(2)H(4)Br(2)分解为 C(2)H(4)的反应受到阻碍，且没有形成含氧碳氢化合物。氧原子的存在还增加了第二层分子的吸附能。
