Optische Kernspin Polarisation (ONP) in Anthracen dotiert mit Phenazin im Temperaturbereich 1,4…300 K / Optical Nuclear Polarisation (ONP) in Anthracene doped with Phenazine in the Temperature Range 1.4…300 K

ONP of proton spins in anthracene doped with 1000 ppm phenazine has been measured as a function of the external magnetic field Hp and its orientation with respect to the crystalline axes for the temperatures: 300, 78, 4.2 and 1.4 K. At 300 K characteristic features in magnetic fields up to 150 G are similar to results observed in doped fluorene crystals. They are interpreted as due to ONP as a consequence of level anti-crossing (LAC) in the triplet state of guest-host complexes. The zero-field splitting tensor is: D*= ±0.0101 (2) cm-1, ∣E*∣≲∣ ± 0.000811 cm-1 with the principal axes z* ∥ b, y* and x* in the ac-plane with ∢ (y*, a) =30 + 1°. No complex formation is observed at or below 78 K. The most prominent feature at all temperatures is the field dependence of ONP when the magnetic field is oriented along the projection of the long molecular in-plane axes of the anthracene molecules. The excitable triplet states in the doped anthracene crystal are discussed in terms of their qualification as ONP-active states