For CF3I adsorbed on Ag(111), reactions stimulated by 100 eV electrons are characterized by temperature programmed desorption (TPD) and reflectionâabsorption infrared spectroscopy (RAIRS). In the absence of electron irradiation, multilayers desorb at 100 K, two orientations in the first layer desorb at 110 and 128 K, and CF3 radical desorption occurs at 300 K. After electron irradiation of coverages below one layer [θ < 0.30 monolayer (ML)], the remaining parent desorption is broadly distributed between 110 and 225 K, there is a C2F5 radical desorption peak at 340 K and the 300 K CF3 radical desorption is replaced by a peak at 240 K. At coverages greater than 0.30 ML, TPD after electron irradiation reveals two new products (CF2I2 and C2F3I) formed in roughly equal amounts. RAIRS suggests that adsorbed CF2I2 has C2v symmetry with both I atoms bound to Ag. We propose that CâC coupling to form C2F5 occurs by insertion of CF2+ or CF2, formed by impact ionization of the parent, into adsorbed CF3, previously formed during either adsorption or the earlier stages of electron irradiation. CF2I2 formation is described in terms of two possible processes: (i) formation of Iâ, which reacts with neighbouring CF3I, and (ii) CâF fragmentation of CF3I+, formed in multilayers, into CF2I+, which reacts with previously formed atomic iodine. At 0.75 ML, the cross-section for loss of CF3I by all removal processes is 1.1 ± 0.2 à 10â16 cm2, whereas that for CF2I2 formation is ca. 10â17 cm2.
对于吸附在 Ag(111) 上的
CF3I,100 eV 电子激发的反应是通过温度编程解吸(
TPD)和反射吸收红外光谱(RAIRS)来描述的。在没有电子辐照的情况下,多层在 100 K 时解吸,第一层的两个取向在 110 K 和 128 K 时解吸,
CF3 自由基在 300 K 时解吸。当覆盖层大于 0.30 ML 时,电子辐照后的
TPD 显示有两种新产物(
CF2I2 和
C2F3I)形成,数量大致相同。RAIRS 表明,吸附的
CF2I2 具有 C2v 对称性,两个 I 原子都与 Ag 结合。我们认为,CâC 耦合形成
C2F5 是通过将母体撞击电离形成的
CF2+ 或
CF2 插入到吸附的 中发生的, 之前是在吸附或电子辐照的早期阶段形成的。
CF2I2 的形成有两种可能的过程:(i) Iâ 的形成,它与邻近的 发生反应;(ii) 在多层中形成的 + 的 CâF 断裂成
CF2I+,它与之前形成的原子
碘发生反应。在 0.75 ML 条件下,通过所有去除过程损失 的横截面为 1.1 ± 0.2 à 10â16 cm2,而形成
CF2I2 的横截面约为 10â17 cm2。