Electron-stimulated desorption of H- from condensed-phase deoxyribose analogues: Dissociative electron attachment versus resonance decay into dipolardissociation

We report the 5-40 eV electron-stimulated desorption (ESD) yields of H- fro m thin films of the DNA backbone sugarlike analogues tetrahydrofuran (I), 3 -hydroxytetrahydrofuran (II), and alpha-tetrahydrofurfuryl alcohol (III), a s well as ESD yields from submonolayer amounts of these compounds condensed on multilayer Ar films, For the pure disordered solid films, our results c orroborate the previous observation of a peak in the H- yield function at a n incident electron energy, E-i, of similar to 10 eV attributed to dissocia tive electron attachment (DEA) along the CH bonds via the formation of a co re-excited resonance. For II and III, a second low-energy peak is also obse rved in the H- ESD yield function. This peak appears near an E-i of 7.3 eV as a weak shoulder superimposed on the low-energy side of the 10 eV structu re; it is associated with a core-excited Feshbach resonance leading to H- p roduction via DEA to the OH substituent. For each of the three molecules, w e observe near 23 eV a third broad peak in the H- ESD yield functions. Meas urements of the H- yields, as a function of the coverage of thin Ar spacer films by I, II, and III, suggest that the 23-eV peak is not due to multiple electron scattering, but results from direct transient anion formation abo ve the dipolar dissociation threshold. These results, combined with those r ecorded at higher Ar spacer thickness, indicate that the 23-eV peak arises principally from decay of a transient anion (or anions) into an electronic excited state (or states), which dissociates into H- and the corresponding positive ion radical.