Exciton transitions in crystalline anthracene for k perpendicular to the b axis

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Abstract
The energy and oscillator strength of exciton transitions with wave vector k perpendicular to the b crystal axis of anthracene are calculated using the second quantized boson theory and compared with the results of reflection spectroscopy. The lattice sums of intermolecular interactions used in the calculations have a dipole component, computed using Ewald's method, and a nondipolar higher multipole part. The latter was obtained by rescaling the lattice sums of Silbey, Rice, and Jortner who calculated the exciton interactions using Pariser wavefunctions. The calculations are compared with the reflection spectra of faces (001) and (201̄) obtained by Clark. Inclusion of the nondipolar interaction leads to substantial improvement in the agreement of theory with experiment. Predictions are made for wave vectors with directions k perpendicular and parallel to the long (L) axis of the molecule as well as for another direction intermediate between the normals to the (001) and (201̄) planes.
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