ESR Evidence for Proton Tunneling from a Positive Hole through Intermolecular Hydrogen Bond in Irradiated Single Crystals of Carboxylic Acids

Abstract

It has been found that an irradiated single crystal of potassium hydrogen fumarate‐d 2 ( K + − OOC–CD =CD–COOH ) gives two kinds of carboxyl radical, − OOC–CD=CD–COO · [ O σ ( I )] and · OOC–CD=CD–COOH [ O σ ( II )] . Evidence has been obtained for O σ ( I ) being formed from the positive hole at the COOH end by protontunneling to the neighboring COO− group through the intermolecular hydrogen bond. The dipolar tensor calculated for the transferred proton agrees well with the observed tensor in both the principal values and directions. O σ ( II ) formed by loss of an electron from the COO− group gives the hyperfine coupling to the proton which belongs to the neighboring COOH group. Agreement between the observed and calculated dipolar tensors is also fairly good.