Pure electronic, vibronic, and two-particle surface excitons on the anthracene crystal. II. Experimental study and analysis of the (0,1) region

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Abstract
In this second part, we present the experimental and theoretical study concerning vibronic surface transitions for the vibration modes 390 and 1400 cm−1. We begin by a theoretical discussion of the different limiting cases of exciton‐vibration coupling. In the experimental part, evidence of the surface character for the observed structures in surface emission excitation spectra is provided by their shifts upon surface coating. A general smilarity of the surface states with the previously described bulk states, including a translational equivalence (δ̄=206 cm−1), is established. The observed structures are assigned to interacting single particle (vibron) resonances and two‐particle bands. However, some slight discrepancies between surface and bulk band structures lead us to question the complete validity of their translational equivalence. Finally, our observations show that the surface two‐particle excitation profile (peak shaped) is quite different from the surface two‐particle absorption profile (stepwise threshold profile). We propose a model mechanism of the surface excitations relaxation which accounts qualitatively for this specific surface excitation profile.