Optical dipole coupling mechanism

However, it is necessary to determine precisely the orientation of the dipole moments, and to ensure that the observed CD is not the resultant from a mixture of con formers. Moreover, even with a correct choice of the dipoles, there are often shortcomings. For instance, studies of l,l -spirobisindanes have shown substantial discrepancies between the theoretical and experimental results for several products of known configuration 27). It has been shown that the signs of the bands stand in direct relation to the configuration of the spiro-atoms, which means that the optical activity is really governed by the coupling mechanism including other types of interaction. 

Optical excitation transfer can occur between molecules as much as 10 nm apart when the dipole-dipole coupling between molecules (one excited "photon donor" chromophore, the other an unexcited "photon acceptor" chromophore) by a mechanism known as Forster79 resonance transfer or fluorescence resonance energy transfer (FRET) its characteristic dependence on the distance r between the two chromophores is r 6. 

The application of coupled oscillator and related theories to the investigation of nucleic acids and polynucleotides has been reviewed by Brahms. The optical activities of single nucleosides and derivatives have been calculated by a coupled oscillator theory in which the tt-tt transitions of the bases were decomposed into individual bond-bond transition moments which were then coupled by the dipolar coupling mechanism. Apparently such a treatment was necessary to account for deficiencies in the simple approach of chromophore-centered dipole transition moments. 

Electric dipole-dipole coupling is the strongest if the corresponding optical transitions in both molecules are allowed for electric dipole radiation. This is not the case of triplet-energy transfer (Figure 15.2), which must follow an alternative mechanism. Dexter proposed that for such cases it is necessary to include explicitly the spin wavefunctions in the matrix element of the perturbation, eq. (15.21). The molecular wavefunction ij/ is expressed as the product of a spacial cp(f) and a spin electronic wavefunction... 

The p-m Mechanism. In this instance, one chromophore contains the electric dipole transition and another contains the magnetic dipole transition. These are coupled in the molecule to produce optical activity in both transitions. 

V. Kerasek, O. Brzobohaty, P Zemanek, Longitudinal optical binding of several spherical particles studied by the coupled dipole method. J. Opt. A Pure Appl. Opt. 11 (2009) 034009. P.A.M. Dirac, The Principles of Quantum Mechanics, Oxford University Press, Oxford, 1958. 

Two MO calculations have been performed on the dimer (NO>2. Vladimiroff has concluded that a cyclic structure is most stable. Shancke and Boggs carried out an ab initio calculation on the cw-isomer and expressed reservation about some of the geometrical parameters calculated by Vladimiroff and the strongly contracted basis set he used. In an additional mechanism for the spin-forbidden a II-x II transition of nitric oxide, consideration has been given to the coupling of two NO molecules and the subsequent co-operative optical transition via a one-photon, spin-allowed, electric-dipole mechanism. It was concluded that this co-operative mechanism is as important as the conventional spin-orbit interaction mechanism. 

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