TnFrequency Functions as Energy Contours for Photon Absorbance in Condensed Systems

摘要

Spectroscopic absorption contours of condensed systems appear to be described by one of several frequency functions, i.e., Gaussian, Lorentzianlpar;T1rpar;, orTn, where1thinsp;thinsp;nthinsp;le;thinsp;3. A phenomenological explanation is given in terms of a statistical model involving random perturbations on energy levelslpar;lang;psgr;mverbar; H verbar; psgr;nrang;,lang;psgr;nverbar; H verbar; psgr;nrang;rpar;and orthogonal coupling matrix elementslpar;lang;psgr;mverbar; Mqverbar; psgr;nrang;rpar;, whereMqis the lighthyphen;coupling operator andnandmare the two states between which transitions occur. If the matrix elements are well shielded from perturbation or strong complexes exist such that only a few relaxations of the same order of duration can occur, Gaussian functions result. If, along with the energy levels, one of the orthogonal components is strongly perturbed by a statistically orientated environment, a Lorentzian functionlpar;T1rpar;results. If two such components are perturbed, the predicted function isT2, and if all three components are significantly perturbed, thenT3results.