The 4000 Å transition of crystal anthracene

New low temperature determinations of ?₂(ω) for crystal anthracene locate the 0-0 transition origin at 25096 ± 6 cm^?1 for the b-polarization. There is no Stokes shift of the fluorescence origin. The exciton bands which are optically accessible by probing the (ab) crystal face with normal incidence light polarized either parallel or perpendicular to the b-axis have a temperature dependent splitting. The Davydov splitting at 77°K is 267 ± 12 cm^?1. The temperature dependence of the k = 0 polariton splitting and the exciton bandwidths (b-polarization and a-polarization) are also given and together with the Davydov splitting provide a test of the adequacy of theories of exciton interactions. The polarization ratio measured as the ratio of the oscillator strengths of the two transitions (f_b/f_a) is quite temperature dependent for both the region of the (0-0) transition and over the total vibronic transition. At 77°K, the value of f_b/f_a is 8.0 for the origin region close to that expected of an oriented gas but is 4.5 over the total transition. Some spectral structure observed only in the b-polarized reflectance spectrum at temperatures less than 77°K is related to the existence of defects localized near the surface.