Anthracene weak intensity bands

In Figure 12.2, a diffuse-reflection spectra recorded from anthracene is shown in two representations spectrum (a) gives the K-M function, and spectrum (b) shows the reflection-absorbance for the relative diffuse reflectance r, that is, -logr. By comparing the two spectra, it is clear that the intensities of relatively weak absorption bands are enhanced in spectrum (b). 

Electron transfer was mediated by metallic silver colloids whose surfaces contained either a strong (SH ) or a weak (CN ) nucleophile [531]. The former case is illustrated by changes in the absorption spectrum of a 1.0 x 10 4 M, deaerated solution of metallic silver particles, subsequent to the consecutive addition of 2.0 x 10 4 M NaSH and 3.0 x 10-4 M anthracene quinone sulfonic acid, AQS (Fig. 85) [506]. The origin of the intensity decrease and the broadening of the silver plasmon absorption band upon the addition of nucleophilic SH is incompletely understood. However, that an absorption... 

Figure 27. UV spectra of anthracene and the ring fused bis-anthracene (ref. 2). On the anthracene structure are shown the in-plane orientations of the electric dipole transition moment vectors associated with the intense short wavelength UV bands (1Bb) near 250 nm and the weak long wavelength bands ( LJ near 360 nm. The Xmax for the exciton bands of bis-anthracene are red shifted from the corresponding bands in the parent, as the vectors intersect at >90°.

In most organic crystals, however, the first absorption regions are less Intense and show weak coupling characteristics. In the anthracene crystal, for instance, the vibronic envelope of that transition is nearly the same as in solution. However, the vibronic bands are individually split, each into two components, with separations from 100-200 cm . With some reservations we may say that the vibronic interaction energies between nearest neighbours in the lattice are of the same order of magnitude. 

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