The Electronic Structure of Copper Dichloride (CuCl2)

元素周期表中的过渡元素的特征是存在部分填充的d壳层。含有这种跃迁元素的分子具有复杂的电子结构，因为将电子从一个d轨道移动到另一个d轨道只需要很少的能量。因此，无论是在理论上还是在实验上，这些分子的电子性质都不容易研究。结晶二氯化铜，CuCl2.4H20，是一种稳定的黄色固体。然而，在加热时，结晶水被煮沸，留下三原子分子CuCl2，这是一种化学上不稳定的开壳态分子（自由基）。尽管它的体积很小，但它具有复杂的电子结构。近十年来，用光谱学方法对其性质的实验测量取得了一些进展。迄今为止，对其结构的理论计算还没有给出可靠的结果。CuCl2的电子结构被认为是过渡金属二卤化物中最简单的，因为它实际上只有一个未配对电子（d9构型）。这个电子的自旋相对于基电子态的轨道角动量有两种可能的方向；因此，有两种不同能量的状态，即所谓的自旋分量。到目前为止，对CuCl2的所有实验观察都涉及到这两种状态中较低的分子；因此，它们之间的能量分离是未知的。本建议的目的是衡量这种分裂。确定这个量是很重要的，因为：(i)分离本身是有意义的，因为它提供了CuCl2电子结构的信息；（ii）分离的知识将允许分析更高振动水平的扰动；（ii）分裂的实验测量提供了一个基准值，以指导CuCl2电子性质的理论计算。

The transition elements in the periodic table are characterised by the presence of partially filled d-shells. Molecules that contain such a transition element have a complicated electronic structure because it takes very little energy to move an electron from one d-orbital to another. In consequence, the electronic properties of such molecules are not straightforward to study, either theoretically or experimentally.Crystalline copper dichloride, CuCl2.4H20, is a stable, yellow solid. However, on heating, the water of crystallisation is boiled off to leave the triatomic molecule CuCl2 which is a chemically unstable molecule in an open-shell state (a free radical ). Despite its small size, it possesses a complicated electronic structure. Some progress has been made in the last ten years on experimental measurements of its properties by spectroscopic methods. Theoretical calculations of its structure have not given reliable results so far. The electronic structure of CuCl2 is expected to be the simplest of the transition metal dihalides because there is effectively only one unpaired electron (d9 configuration). The spin of this electron has 2 possible orientations relative to the orbital angular momentum in the ground electronic state; as a result, there are two states of different energy, the so-called spin components. All experimental observations of CuCl2 so far have involved the molecule in the lower of these two states; consequently, the energy separation between them is not known. The objective of the present proposal is to measure this splitting. It is important to determine this quantity because:(i) the separation is of interest in its own right because it gives information on the electronic structure of CuCl2,(ii) knowledge of the separation would allow perturbations in higher vibrational levels to be analysed and(ii) an experimental measurement of the splitting gives a benchmark value to guide theoretical calculations of the electronic properties of CuCl2.