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

We report the 5-40 eV electron-stimulated desorption (ESD) yields of H- from thin films of the DNA backbone sugarlike analogues tetrahydrofuran (I), 3-hydroxytetrahydrofuran (II), and alpha-tetrahydrofurfuryl alcohol (III), as well as ESD yields from submonolayer amounts of these compounds condensed on multilayer Ar films, For the pure disordered solid films, our results corroborate the previous observation of a peak in the H- yield function at an incident electron energy, E-i, of similar to 10 eV attributed to dissociative electron attachment (DEA) along the CH bonds via the formation of a core-excited resonance. For II and III, a second low-energy peak is also observed 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 structure; it is associated with a core-excited Feshbach resonance leading to H- production via DEA to the OH substituent. For each of the three molecules, we observe near 23 eV a third broad peak in the H- ESD yield functions. Measurements 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 above the dipolar dissociation threshold. These results, combined with those recorded 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.