CHARACTERIZATION OF ELECTRONIC TRANSITIONS IN COMPLEX MOLECULES
CHARACTERIZATION OF ELECTRONIC TRANSITIONS IN COMPLEX MOLECULES
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DOI：
10.1039/df9500900014
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发表时间：
1950-01-01
期刊：
影响因子：
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通讯作者：
KASHA, M
中科院分区：
文献类型：
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作者：
KASHA, M
本文总结了在合适的系统中对复杂分子在光激发下的发射特性的研究可能得出的结论类型。讨论了复杂分子中无辐射跃迁的类型，并给出了一个光谱判据：给定多重度的发射能级是该多重度的最低激发能级。描述了复杂分子中的相互作用，并指出它们的重要性源于三重态激发的高概率——这一结论与几年前的光谱学思想趋势背道而驰。根据麦克卢尔的说法，提出了一个原子序数标准，通过研究复杂分子中重原子取代的跃迁强度，可以确定相互组合。最后，列出了一份经验标准清单，允许区分纯n电子跃迁（T-+ n-*）和涉及激发非成键n、0和S原子电子到反成键T分子轨道（n 3n *）的跃迁。这些标准中最确定的是在酸性介质中n-+ n*跃迁的消失。报道了n—f n*跃迁的自旋轨道耦合过程的异常增强，并给出了可能的解释。通过对光激发下复杂分子的发射特性的研究，可以获得有关复杂分子电子态的许多有用信息。在特殊情况下，可能有必要在液氮温度下研究刚性玻璃溶液中的分子，以观察其发光特性。然而，由于几乎没有不能以中等量子效率观察到光发射的情况，因此发射光谱的方法几乎可以普遍应用。这些研究所得的信息是对真空紫外吸收光谱、蒸气高分辨率光谱和溶液吸收光谱所得信息的重要补充。在作者即将出版的一系列出版物中，详细报道了复杂分子发射光谱的研究。本文总结了这类调查所揭示的信息类型。
A summary is given of the types of conclusions which may be drawn from a study of the emission properties of complex molecules under optical excitation in suitable systems. The types of radiationless transitions in complex molecules are discussed, and a resultant spectroscopic criterion stated: The emitting level of a given multiplicity is the lowest excited level of that multiplicity. Intercombinations in complex molecules are described, and their importance is shown to arise from the high probability of the excitation of triplet states-a conclusion which runs counter to the trend of spectroscopic thought of a few years ago. An atomic number criterion is stated (after McClure) which permits the identification of intercombinations by a study of intensity of the transition with heavy atom substitutions in a complex molecule. Finally, a listing of empirical criteria is made which permits a distinction between pure n-electron transitions (T-+ n-*) and transitions involving excitation of non-bonding N, 0, and S atom electrons to anti-bonding T molecular orbitals (n 3 n*). The most definitive of these criteria is the disappearance of n-+ n* transitions in acid media. An unusual enhancement of the spin-orbit coupling process for n--f n* transitions is reported and a possible interpretation is given.Much useful information concerning the electronic states of complex molecules can be gained from a study of the emission properties of such molecules under optical excitation. In particular cases it may be necessary to study the molecule in rigid glass solutions at the temperature of liquid nitrogen in order to observe its light emission properties. However, since there is hardly a case in which light emission can not be observed with a moderate quantum efficiency, the method of emission spectroscopy can be applied almost universally. The information derived from such studies forms an essential supplement to that obtained from absorption spectra in the vacuum ultra-violet, high resolution spectra of vapours, and absorption spectra of solutions. In a series of forthcoming publications by the writer a detailed study of emission spectroscopy of complex molecules is reported. 1 The present paper summarizes the type of information revealed by such investigations.