Electron Paramagnetic Resonance Analysis of Damage Center in a Gamma‐Irradiated Bicyclo[2.2.1]Hept‐5‐Ene‐2,3‐Dicarboxylic Anhydride Single Crystal

Gamma irradiation effects on single crystals of bicyclo[2.2.1]hept‐5‐ene‐2,3‐dicarboxylic anhydride were investigated by angular‐dependent single‐crystal Electron Paramagnetic Resonance (EPR) spectroscopy. Irradiation with a 60 Co source resulted in the formation of a stable carbon‐centered radical, whose magnetic properties were characterized through systematic rotation of the crystal. The principal components of the anisotropic g‐tensor and hyperfine interaction tensors were determined from orientation‐dependent spectra. Two distinct hyperfine splitting patterns ( β and γ ) were resolved, indicating interactions of the unpaired electron with different sets of − C 2 H 2 protons within the constrained molecular framework. The orthorhombic crystal symmetry enabled reliable correlation between tensor principal values and crystallographic axes, strengthening the structural assignment of the radical center. The results demonstrate that the rigid norbornene‐bridged framework significantly influences spin localization, tensor anisotropy, and radical stability. Overall, this study highlights the combined role of molecular rigidity and crystal symmetry in governing radiation‐induced defect formation and establishes a clear structure–property relationship in organic anhydride crystals.