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

The second stable radical, NH(3)(+)C()(CH(3))COO(-), R2, in the γ-irradiated single crystal of l-alanine and its fully (15)N-enriched analogue were studied by an advanced pulsed EPR technique, 2D-HYSCORE (two-dimensional hyperfine sublevel correlation) spectroscopy at 200K. The nitrogen hyperfine coupling tensor of the R2 radical was determined from the HYSCORE data and provides new experimental data for improved characterization of the R2 radical in the crystal lattice. The results obtained complement the experimental proton data available for the R2 radical and could lead to increased accuracy and reliability of EPR spectrum simulations.