The theory of the gross vibrational
structure in the electronic spectra of molecular aggregates is developed for
the case of weak intermolecular interaction. The electronically excited states
are represented by a set of m-m functions corrected to first order as described
in Part IV of this series.
An explicit treatment is given for
aggregates with two molecules per unit cell. Formulae are obtained for the
relative vibronic intensities, splittings, and polarization ratios in
absorption spectra, and for relative quantum yields and polarization ratios in
fluorescence spectra.
The theoretical results are compared with
those of the E-V coupling theory developed in Parts II and III. On the basis of
this comparison, a general equation is put forward to relate the theoretical
crystal splitting (i.e. the splitting for a rigid model) to observed
polarization ratios in spectra.
The theoretical results are compared with
the observed vibrational structure in the 3800 Ǻ band system of anthracene
crystal. The crystal splitting calculated from the observed polarization ratios
is 380 cm-1. The theory accounts, within the rather large
experimental error, for the observed variations of polarization ratio in both
the absorption and the fluorescence spectra of anthracene crystal.
