Investigation of the nitrogen hyperfine coupling of the second stable radical in γ-irradiated l-alanine crystals by 2D-HYSCORE spectroscopy

► Second stable radical of γ-irradiated l-alanine-14N was investigated by pulse EPR. ► The nitrogen hyperfine tensor of the second radical was determined by HYSCORE. ► Assignation was confirmed with γ-irradiated l-alanine-15N by HYSCORE. ► Experiment supports prediction that the carbon atom transforms from a sp3 to sp2.