Relaxation of (CS2)2(-) to its global minimum mediated by water molecules: photoelectron imaging study.
Relaxation of (CS2)2(-) to its global minimum mediated by water molecules: photoelectron imaging study.
复制标题
由水分子介导的 (CS2)2(-) 弛豫至其全局最小值：光电子成像研究。
DOI：
10.1021/jp806478g
复制
发表时间：
2008
期刊：
影响因子：
--
通讯作者：
A. Sanov
中科院分区：
文献类型：
--
作者：
T. Habteyes;L. Velarde;A. Sanov
通过355和266 nm的光电子成像研究了（CS2）2（-）的几种异构体的共存。通过理论计算，将光电子能谱中的谱带归属于CS2（-）、CS2离子-分子复合物（Cs对称，（2）A'电子态）和两个共价键合的二聚体-阴离子结构：C2 v（（2）B 1）和D2 h（（2）B 3 g）。异构体分布敏感地取决于离子源条件，特别是前体气体混合物中水的存在。光电子带的强度变化表明，水的存在促进了整体最小C2 v（（2）B 1）结构的形成，特别是相对于亚稳态（局部最小）离子-分子复合物.这一趋势有两个合理的假设。第一个是在团簇形成阶段H2O的存在有利于从CS2（-）+CS2渐近线开始时达到全局最小二聚体-阴离子平衡所必需的非绝热转变。第二个是，在水的存在下形成的初始集群往往有，平均而言，更多的内部能量，这是需要克服的势能障碍，从全球最小结构的亚稳平衡。当共价键形成时，过量的溶剂分子从簇中蒸发，产生稳定的（CS 2）2（-）二聚体阴离子。在（CS 2）n（-），n >或= 3和（CS 2）2（-）（H2 O）m，m > 0簇中，由于溶剂与单体-阴离子更有利的相互作用，共价-二聚体核心结构的数量急剧减少（即，CS 2（-））核心。
The coexistence of several isomers of (CS 2) 2 (-) is examined via photoelectron imaging at 355 and 266 nm. Assisted by theoretical calculations, the bands in the photoelectron spectra are assigned to the CS 2 (-).CS 2 ion-molecule complex ( C s symmetry, (2)A' electronic state) and two covalently bound dimer-anion structures: C 2 v ( (2)B 1) and D 2 h ( (2)B 3g). The isomer distribution depends sensitively on the ion source conditions, particularly the presence of water in the precursor gas mixture. The intensity variation of the photoelectron bands suggests that the presence of water enhances the formation of the global-minimum C 2 v ( (2)B 1) structure, particularly relative to the metastable (local-minimum) ion-molecule complex. This trend is rationalized with two assumptions. The first is that the presence of H 2O at the cluster formation stage facilitates the nonadiabatic transitions necessary for reaching the global-minimum dimer-anion equilibrium when starting from the CS 2 (-) + CS 2 asymptote. The second is that the initial clusters formed in the presence of water tend to have, on average, more internal energy, which is needed for overcoming the potential energy barriers separating the metastable equilibria from the global-minimum structure. As the covalent bonds are formed, excess solvent molecules are evaporated from the cluster, giving rise to stable (CS 2) 2 (-) dimer anions. In the (CS 2) n (-), n >or= 3, and (CS 2) 2 (-)(H 2O) m , m > 0, clusters, the population of the covalent-dimer core structures diminishes drastically due to more favorable solvent interactions with the monomer-anion (i.e., CS 2 (-)) core.