Optical polarizability tensor and absorption tensor in (fluoranthen) 2PF 6

Abstract

The indicatrix orientation, the transmission spectra polarized parallel to the principal axes (and also to various directions between these axes), and the birefringence were measured in small crystal of (Fluoranthen) 2PF 6 in the NIR and VIS spectral range. The results are discussed with regard to the orientation of the Fluoranthen molecule axes and the arrangement of the intermolecular C-C and C-F contact directions. Strong excitations as well intramolecular as intermolecular (charge transfer) are observed in all principal directions in contrast to the pure Fluoranthen crystal. The sign of the birefringence is large negative owing to the plate like Fluoranthen molecules. The refractive indices n γ and n β are found lying in the molecule plane and are near to one another n γ ≈ n β and considerably greater than n α normal to the plane (stack direction). In the VIS a n γ-dispersion is observed yielding a strong dispersion of the optic axial angle. The axial angle decreases and becomes zero (n γ = n β ) in a small spectral range near 640 nm, i. e. in this range the crystal is uniaxial and has optically a higher symmetry than the true symmetry (monoclinic). Just in this spectral range also the plasma edge was found by reflexion spectroscopy.