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Time‐dependent quantum theory II. Absorption of light by dimers: Quantum theory and classical analogy
Author(s) -
Schurr J. M.
Publication year - 1971
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560050104
Subject(s) - polarizability , excited state , degenerate energy levels , quantum mechanics , dipole , quantum , physics , field (mathematics) , excitation , wave function , chemistry , atomic physics , molecule , mathematics , pure mathematics
The quantum theory of light absorption by a pair of neighboring absorbers is developed in the point dipole approximation for the circumstance where excited states decay only by radiative damping. Comparison with classical local field theories, in which the monomers are represented by constant, frequency‐dependent complex polarizabilities, shows that these local field theories are valid for non‐harmonic absorbers only in the weak interaction limit, and only when there exist no states with both monomers simultaneously excited (e.g. one excited vibrationally, the other electronically) that are nearly degenerate with the single excitation states and also connected to them by appreciable transition moments. Failure of the local field theories is, thus, shown to be a consequence of the non‐harmonic nature of real absorbers. Using a general relation between the level‐shift function and complex polarizability, a recipe is formulated for calculating the complex polarizability and spectrum of a dimer.