Reactive Scattering of 1−5 eV O- in Films of Tetrahydrofuran

Abstract

An understanding of all nascent events leading to radiolytic DNA damage is required to achieve a complete description of ionizing radiation effects on living cells. These early, subpicosecond events involve mainly low-energy (E < 20 eV) secondary electrons (SE) and low-energy (E < 5 eV) secondary ion (and neutral) fragments; the latter are created either by the primary radiation or by SE via resonant mechanisms, i.e., dissociative electron attachment (DEA). While recent work has shown that 3−15 eV SE initiate DNA strand break formation exclusively via resonances, the subsequent damage induced by the energetic DEA ion fragments in DNA or its basic components is unknown. Here, we report 0−20 eV electron impact measurements of negative ion desorption from condensed films containing O2 and tetrahydrofuran, C4H8O (THF), a deoxyribose analogue. Our experiments show that all of the OH- and some of the H- desorption yields are the result of reactive scattering of the 1−5 eV O- fragments produced initially by DEA to O2. These O- reactions involve hydrogen abstraction and atom exchange from THF, and result in the formation of THF-yl radicals, as well as THF oxidation products, most likely lactones and alkoxyl radicals. O- scatters over nanometer distances comparable to DNA dimensions, and reactions involve formation of a transient (OC4H8O)* - collision complex. Our measurements support the notion that in DNA, exposed to ionizing radiation, similar localized secondary ion reactions can be initiated by the abundant secondary electrons, and may result in further clustered damage, lethal chemical transformations, and enhance DNA lesions.