Rotatory strength electronic

A2 + Ea + A + E ) e coupling can lead to mixed polarization within the vibronic CD band envelops of both the Ai A2 and Ai Ea transitions. In the absence of vibronic coupling, the Ai - A2 transition would be polarized parallel to the trigonal axis of the system, whereas the Ai - Ea transition would be polarized perpendicular to the trigonal axis. In the presence of vibronic coupling, vibronic components of both parallel and perpendicular polarization may appear in both the Ai - A2 and Ai Ea CD bands. Secondly, from Eqs. (61) and (62) we see that the net CD associated with the Ajg - Tig transition need not vanish even when the zeroth-order net electronic rotatory strength, r(°(Ai A2) + r(° Ai - Ea), is zero. 

The induced magnetic dipole moment has transformation properties similar to rotations Rx, Rt, and Rz about the coordinate axes. These transformations are important in deducing the intensity of electronic transitions (selection rules) and the optical rotatory strength of electronic transitions respectively. If P and /fare the probabilities of electric and magnetic transitions respectively, then... 

Another open area is the assignment of the various electronic transitions observable in the absorption, CD, and ORD spectra. Owing to the fact that bands in chiroptical spectroscopy have opposite signs, maxima can be more easily identified in CD and ORD spectra than in absorption spectra. Also, such information as the rotatory strength can be used for band assignment, a necessary condition for a widespread use of chiroptical spectroscopy for correlation of configurations. 

The COSMO solvent model has been used to simulate the influence of water on the electronic spectrum of A -methylacetamide [81], and the results was compared with the results of molecular dynamics simulations (where the electronic spectrum were calculated as an average over 90 snapshots from MD simulations). Most of the hydration effects were found to come from the first solvation shell hydrogen-bonded water molecules, and the continuum model does not properly account for these effects. The rotatory strengths were not calculated directly in ref. [81]. However, the results were used to model ECD spectra of peptides via the coupled oscillator model, with satisfactory result. 

The ellipticity, or the intensity of the circular dichroism (CD) spectrum, is fundamentally characterized by the rotatory strength R, which is given by the imaginary part of the inner product between the electronic and magnetic dipole transition moment vectors ... 

Thus, the rotatory strength R is able to be regarded as an analog of the oscillator strength/in UV spectroscopy. Nevertheless, practically no systematic study has been carried out on the effects of electronic and magnetic interactions on the rotatory strength R of cyclophanes. 

In quantum theory the quantity characterizing the Cotton effect of a given electronic transition 0 ->i is the rotatory strength Ro/- It corresponds to the scalar product of the electric (/Iqi) and magnetic (moj) transition moments of that excitation ... 

---