External Heavyhyphen;Atom Spinhyphen;Orbital Coupling Effect. I. The Nature of the Interaction

摘要

The effect of external heavyhyphen;atom spinhyphen;orbital coupling perturbation has been studied in the lowest energy tripletlarr;singlet absorption spectrum of various 1hyphen;halonaphthalenes in 1:1 molar 1hyphen;halonaphthalene: alkyl halide binary solutions. It is shown that the interaction prerequisite to the charge transfer which must occur in these systems is probably of a donormdash;acceptor nature, the alkyl halide functioning as the acceptor and the 1hyphen;halonaphthalene functioning as the donor. Steric effects are estimated using molar refraction data and are undoubtedly of importance, particularly when the alkyl halide contains more than one halogen atom.Theexternalheavyhyphen;atom effect is spinhyphen;orbital coupling in nature as may readily be seen by comparison of the enhancements induced in the Tlarr;S absorption of the 1hyphen;halonaphthalene by various alkyl halides; the order of enhancement is alkyl iodidealkyl bromidealkyl chloride and follows roughly the order of the atomic spinhyphen;orbital coupling factors squared. Theexternalheavyhyphen;atom effect is greater the larger theinternalheavyhyphen;atom effect, as is shown both experimentally and theoretically. In fact, anexternalbromine is more effective than aninternalfluorine, while anexternaliodine is more effective than aninternalchlorine, and roughly comparable in enhancement ability to aninternalbromine. Simple theoretical considerations enable one to deduce the singletmdash;triplet mixing coefficients for both theexternalandinternaleffects, and to validate the spinhyphen;orbital coupling nature of the effect.