Search for a Trapped Hole in an Irradiated Crystal of L-Alanine by the ESR Technique

Crystals of L-alanine, CH3CHNH3+CO2−, and also CH3CHND3+CO2−, CH3CDNH3+CO2−, and CH3CDND3+CO2− were irradiated at 80°K, and their ESR absorptions were observed at the same temperature. Most of the observations were made at 9 GHz, although some observations were made at 24 and 35 GHz. In addition to the known absorption from the trapped electron (or anion), an absorption with many peaks was detected and was attributed to the trapped hole (or cation) of L-alanine. From the hfs tensor for one of the methyl protons and other evidence, the electron hole was found to be trapped predominately at the C–C bond connecting the methyl group to the α-carbon atom. In the four crystals examined, the concentration of the cation was comparable to that of the anion.