Scaling in Molecular Electronic Spectroscopy: Core-Nonpenetrating Rydberg States

实验物理化学项目支持麻省理工学院的Robert W. Field教授继续研究“标度定律”，这是量子数的先验已知函数。当分子各部分之间的耦合变得足够弱时，这种标度定律就会出现。例如，氢本征态的许多性质可以表示为Z、n和l的简单函数。许多基于原子的标度关系仍然是有用的和有指导意义的，甚至对于多原子分子；对于核-非穿透性分子里德堡态，里德堡电子与分子离子核之间的耦合非常弱，与氢系统的相似性很强。菲尔德将进行各种类型的实验，包括共振增强的多光子电离或多重共振光谱，以努力开发用于核非穿透分子里德伯态光谱研究的实验方法。这些研究将产生关于分子离子核的电各向异性和极化性的信息。对这些实验的实际意义作一些评论是有必要的。为什么我们要关心阳离子的电多极矩？所有的+1阳离子都有相同的单极子，所以阳离子与外界相互作用的主要方面是独立于分子的。另一方面，离子特异性的远程相互作用来源于更高的多极（及其法向坐标位移导数）。这些多极和导数控制了共振远程离子-分子，离子-电子，可能还有离子-表面能和角动量交换的机制和速率。从核心非穿透里德伯态的系统研究中获得的信息将对等离子体中发生的各种过程产生有价值的见解。

The Experimental Physical Chemistry Program supports Prof. Robert W. Field of Massachusetts Institute of Technology in his continuing investigation of `scaling laws,` a priori known functions of quantum numbers. Such scaling laws arise when the coupling between parts of a molecule becomes sufficiently weak. For example, many properties of hydrogenic eigenstates can be expressed as simple functions of Z, n and l. Many atom-based scaling relationships remain useful and instructive, even for polyatomic molecules; for core-nonpenetrating molecular Rydberg states, in which the coupling between Rydberg electron and the molecular ion-core is very weak, the resemblance to hydrogenic systems is quite strong. Field will undertake various types of experiments involving either resonance-enhanced multiphoton ionization or multiple resonance spectroscopies in an effort to develop experimental methods for spectroscopic studies of core-nonpenetrating molecular Rydberg states. These studies will yield information on the electric anisotropies and polarizabilities of molecular ion cores. A few comments about the practical significance of these experiments are warranted. Why should we care about the electric multipole moments of cations? All +1 cations have the same monopole, so this dominant aspect of the interaction of the cation with the outside world is independent of the molecule. Ion-specific long-range interactions, on the other hand, derive from the higher multipoles (and their normal coordinate displacement derivatives). These multipoles and derivatives control the mechanisms and rates of resonant long-range ion-molecule, ion-electron, and possibly ion-surface energy and angular momentum exchange. The information obtainable from systematic studies of core-nonpenetrating Rydberg states would yield valuable insights into a wide variety of processes occurring in plasmas.