EXCEPTIONAL DISPERSION IN DNP CRYSTALS IN THE VISIBLE SPECTRAL RANGE

In DNP monomer crystals the indicatrix, the optic axes angle, the bire fringence, and the absorption tenser were measured in the VIS and NIR spectral range. A crossed-axial-plane dispersion is found with change of the plane orientation in the green region (1.9.10(4) cm(-1)) of the spectrum. Calculations of the polarizability tenser by tensorial addi tion of the bond polarizabilities show that the polarizabilities of th e molecules only can not yield the measured orientation of the indicat rix. Polarizabilities with other orientations must be involved. Assign ing polarizabilities to intermolecular contacts with short distances c an explain the measured behavior.