Fundamental processes of radiation damage of benzene solid studied by Auger electron photoion coincidence spectroscopy

Abstract

C H dissociation is known to be responsible for the formation of radiation damage of hydrocarbon crystals such as color centers or radicals. Recently, Auger electron photoion coincidence (AEPICO) spectroscopy has allowed us to get detailed information on microscopic processes of radiation damage, because AEPICO spectroscopy can pick up only the fundamental processes, excluding effects due to secondary electrons. In this work, in an attempt to study which electronic state is responsible for the C H bond dissociation, AEPICO spectra of benzene solid were measured at 80 K as a function of photon energy. AEPICO measurements were examined at three photon energies, i.e. 285 eV(π *(e 2u) ← 1s), 287 eV(σ *(C H) ← 1s), and 430 eV(ionization← 1s). Relative magnitudes of the AEPICO yield Y(hv), which reflects the C H dissociation yield, were estimated by dividing AEPICO signals with intensities of Auger electron yield. Experimental results showed that Y(287eV)/ Y(430eV)≈ 1, whereas Y(287eV)/ Y(430eV)≈ 0.13. A relation between the small value of Y(287eV)/ Y(430eV) with the small values of the radiation damage yieldη( hv) near 285 eV is discussed. In that case,η(nearKedge)η(overKedge)≈ 0.1∼0.3 [5] [A. Kimura, K. Nakagawa, K. Tanaka, M. Kotani, R. Katoh, Nucl. Instr. and Meth. in Phys. Res. B91 (1994) 67].