PARAMAGNETIC RESONANCE IN L-CYSTEINE HYDROCHLORIDE IRRADIATED AT 77K.

An electron paramagnetic resonance study has been made on a single crystal of L‐cysteine hydrochloride irradiated with a 1.5‐MeV electron beam at 77°K. The hyperfine structure of the main resonance pattern was found to be an almost isotropic double doublet, whereas the g factor was found to be highly anisotropic but axially symmetrical, the principal values being 2.29, 1.99, and 1.99. The main resonance has been attributed to the free radical HOOC–CH–CH2–S.          –         NH3Cl with the unpaired electron occupying one of the two nearly degenerate orbitals of the sulfur atom. A remarkable broadening of the resonance spectrum was observed at elevated temperatures, and evidence is given that this broadening is due to a short spin—lattice relaxation time due to a large spin—orbit coupling in this free radical.