Transition dipole vector

Table 3. Transition Dipole Vector Coupllng-Oxyhemocyanln...

Figure 8.2 Orientation of transition moments of cyanine fluorophores terminally attached to double-stranded DNA. (A) The orientation parameter K2. The transition dipole vectors for the coupled donor and acceptor fluorophore are indicated by the arrows, labeled D and A. Vector A is generated by the in-plane translation of vector A to share its origin with vector D. The definition of K2, given in Eq. (8.5), is based upon the angles shown. (B) If the fluorophores he in parallel planes, the orientation parameter simplifies to K2 — cos2 T and varies between 0 and 1. The schematic shows the limiting cases, where the transition moments are parallel (k2 = 1) and crossed (K2 — 0). If the transition moments are colinear, K2 = 4.

The fact that three peroxide-to-copper charge-transfer transitions are observed in oxyhemocyanin and oxytyrosinase led us to consider the spectral effects of bridging peroxide between two Cu(II) ions. A transition-dipole vector-coupling (TDVC) model was developed that predicts that each charge-transfer state in a Cu-peroxide monomer... 

Fig. 35. Diagrammatic explanation of the transition dipole vector coupling treatment for two possible peroxide bridging geometries, /<-dioxo and ft-monooxo, and comparison to oxyhemocyanin (see text for explanation)...

It is of interest to examine the nature of the motions of a sidechain as large as a tryptophan residue in the protein interior. Reorientation of the transition dipole vector of tryptophan is due mainly to rotation about the C —C(3 and C,3—Cr bonds, which correspond to the x1 and x2 dihedral angles of the side-chain, although larger-scale collective motions of the backbone are also involved. In the protein environment, the fluctuations of x1 and x2 are expected to be anticorrelated so that large variations in the two angles result in a... 

Since the intensity of IR light for s-polarization is very small at the metal surface, only vibrations with a transition dipole component along the surface normal are detected. This necessitates using p-polarized light for the IR beam. The transition dipole vector of the molecule and electric field vector of the IR light must have a non-zero projection on each other, the consequence is that molecules with their transition dipole parallel to the metal are not seen in the SFG spectrum. This effect is referred to as the IR dipole surface selection rule [45,46]. 

When linearly polarized light is absorbed by a sample, the integrated intensity of the absorption band is proportional to the square of the absolute value of the dot product of the transition dipole vector and the electric field vector of the incident radiation [48, 49] ... 

The transition dipole vector for the oligomer s absorption band associated with excitOTi wavefunction Vg is obtained by summing over the monomer transitions ... 

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