Role of defects in radiation chemistry of crystalline organic materials. 1. ESR evidence for electron trapping in the mixed crystals of binary n-alkanes at low temperatures

Abstract

An ESR study has been made on the electron stabilization in the mixed crystals of binary n-alkanes irradiated at 77 and 4 K, as the first step in understanding the role of defects in radiation chemistry. Evidence has been obtained to show that the radiation-induced electrons are trapped in the mixed crystals in contrast to the absence of trapped electrons in the neat n-alkanes, together with the following results on the trapping site. The ESR line width ({Delta}H{sub msl}) of trapped electrons (reflecting the effective defect size) correlates with the chain length difference ({Delta}n{sub c}) between two n-alkanes. An increase of {Delta}n{sub c} gives a higher yield of the trapped electrons probably because of a stabilization due to an expansion of the defect size. The number of defects accessible to the electrons depends on the crystal structures, being slightly larger in triclinic crystal than in orthorhombic crystals. The effect of deuteriation of the molecules on {Delta}H{sub msl} in addition to the above results suggests that the trapping site is a crystalline lattice defect created by inhomogeneous contacts of the different chain length molecules at the layer boundary and that preexisting defects such as voids are necessary for electrons to bemore » trapped in crystalline n-alkanes.« less