The importance of electronically excited states and of the electron spin on the reactivity of metal dimers and small clusters: matrix isolation experiments and quantum chemical calculations

金属和金属氧化物簇模型对于发展多相催化反应的机理概念是非常重要的。大量能量较低的电子激发态在室温下就已经存在，这是簇反应具有高反应活性和选择性的原因。它允许簇灵活地调整其电子结构，使其理想地适合与底物分子的反应。除了气相研究外，借助基质分离技术进行的测量也为这一研究主题做出了重大贡献。矩阵隔离技术非常适合研究这些团簇的电子激发态的反应性。低温（4 - 40k）的基体保证了所有簇首先处于电子基态。光照射可以选择性地激发它们。自制的海德堡矩阵仪就是专门为这类实验设计的。它允许在10 - 25000 cm-1范围内具有高分辨率的吸收测量（红外和可见光-近红外），以及发射测量（拉曼和荧光）。这些星团可以用窄带宽的激光激发。虽然第一个资助期的主要工作是关于团簇在电子基态和能量低激发态下的特征，但第二个资助期的工作几乎完全集中在依赖于电子态的团簇反应性上。第一个资助期的结果和我们小组的其他结果为这些研究提供了基础。对象是钒和氧化钒分子（子项目A）和钛和氧化钛分子（子项目B）。这些分子的电子态已经被详细研究过了。实验工作伴随着量子化学计算。计划进行复杂而耗时的研究，但所有目标都是可以实现的。

Metal and metaloxide cluster models are extremely important to develop mechanistic concepts of heterogenous catalytic reactions. The large number of eneregtically low-lying electronically excited states, that are populated already at room temperature, are responsible for the high reactivity and selectivity of cluster reactions. It allows the cluster to flexibly adjust its electronic structure so that it ideally fits to the reaction with a substrate molecule. Besides gas-phase studies, measurements with the help of the matrix-isolation technique provide significant contributions to this research theme. The matrix-isolation technique is ideally suited to study the reactivity of electronically excited states of these clusters. The low temperatures (4 - 40 K) of the matrix garantee that all clusters are first in their electronic ground state. By light irradiation they can be selectively excited. The Heidelberg matrix apparatus (self-made) is especially designed for such experiments. It allows absorption measurements (IR and vis-NIR) with high resolution in the range 10 - 25000 cm-1, as well as emission measurements (Raman and fluorescence). The clusters can be excited with a laser of narrow bandwidth.While a major part of the work during the first funding period was concerned with the characterization of clusters in their electronic ground state and in energetically low-lying excited states, the work in the second period concentrates almost exclusively on the reactivities of the clusters in dependence of their electronic state. The results from the first funding period and other results from our group provide the basis for these studies. The objects are vanadium- and vanadium oxide molecules (subproject A) and titanium- and titanium oxide molecules (subproject B). The electronic states of these molecules were already studied in detail. The experimental work is accompanied by quantum chemical calculations. Sophisticated and time-consuming studies are planned, but all objectives are achievable.