Kinematic quasi-vacancy Frenkel biexciton in a Davydov multiplet

This paper shows that, as a consequence of paulion-type Frenkel excitons in molecular crystals such as anthracene, with several molecules per unit cel l, bound biexcitons exist in the absence of dynamic exciton-exciton attract ion. The coupling of excitons in ideal crystals of this type is brought abo ut by the same kinematic effect that causes excitons in nonideal crystals t o be localized close to defects such as vacancies. In the excitation spectr um, the resonance peak of the resulting biexciton is found inside a band co rresponding to the sum of the energies of excitons of unlike components of a Davydov doublet, located between the bands of the total energies of excit ons of the like components of the doublet. The corresponding dispersion equ ation is obtained, and the energy and wave function of the biexciton is det ermined. (C) 1999 American Institute of Physics. [S1063-7834(99)01103-X].