Extinction anisotropy measurements

The results of extinction anisotropy measurements are usually represented in the form of the reduced linear dichroism expressed as follows ... 

The slow peak was associated with the dissociation channel that produces an H atom and an X(2) fragment, while the fast peak was identified with the channel that produces the I( 3/2) fragment. From the polarization measurements they could obtain the anisotropy parameter 3, and this along with the TOF spectra could be used to derive the branching ratio between the two channels as a function of wavelength. Combining this information with the measured extinction coefficients, they were able to derive the partial extinction coefficients to the upper states that correlate with each of the channels. A modified 6 approximation was then combined with all of this information to calculate the upper repulsive potential curves that lead to dissociation into these products. Four upper states are involved in the dissociation in this region. The symmetries of these four states are 3nx, fjl, 3no, and The first two states produce... 

Let us consider the anisotropy of polymer system undergoing simple steady-state shear. This situation can be realised experimentally in a simple way (Tsvetkov et al. 1964). The quantity measured in experiment are the birefringence An and the extinction angle x which are defined by formulae (10.19) and (10.20), correspondingly, through components of the relative permittivity tensor. 

Figure 10 shows the optical absorption spectra of the single crystal of all-trans-/3-carotene measured upon irradiation with linearly polarized light parallel to the a- or fc-crystal axis. Large optical anisotropy for the molar extinction coefficient is seen in these spectra. This observation can be explained in terms of the molecular orientation of /3-carotene in the crystal (see Fig. 9). Since the molecular axis of /3-carotene is almost parallel to the fc-axis, the molar extinction coefficients along fc-axis should appear larger than those along a-axis. Based on the symmetry considerations, these spectra can be assigned to the transitions to the (//fc-axis) and B (//a-axis) molecular excitons, as illustrated in Fig. 10 (Chapman etal., 1967).

When an electric field is applied to a chemical system which exhibits both electrical and optical anisotropy, both the c, and the Cj terms in the fundamental Eq. (4.21) may be field dependent. Note that the usual extinction coefficients of optically anisotropic molecules reflect random average values ij of all chromophore orientations of the system when measured with polarized light. 

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