Bond- and Site-Selective Loss of H Atoms from Nucleobases by Very-Low-Energy Electrons (<3 eV)Financial support from the FWF (Vienna), the EU commission (Brussels) through the EPIC Network, and the DFG (Bonn) is gratefully acknowledged

Excess charge deposited on gas-phase thymine (T) and uracil (U) by resonant attachment of low-energy (0–3 eV) electrons induces the loss of hydrogen, which exclusively takes place from the N positions. This bond selectivity can be made site selective by properly adjusting the electron energy. While electrons at 1 eV result in loss of hydrogen from N1, the reaction can be switched to loss of hydrogen from N3 by tuning the electron energy to 1.8 eV. We find that any energy (and charge) transfer is completely blocked when the N H bond is replaced by N CH3. The present results have significant consequences for the exploration of the initial molecular processes leading to DNA damage, specifically in relation to recent observations of strand breaks in plasmid DNA induced by very low energy (0–4 eV) electrons. Recent gas-phase experiments on the isolated nucleobases (NBs) thymine (T), cytosine (C), adenine (A), guanine (G), and uracil (U) have demonstrated that they all effectively capture low-energy electrons in the range below 3 eV . The generated transient negative ion (TNI) subsequently decomposes by the loss of a neutral hydrogen atom. The overall dissociative electron attachment (DEA) reaction can be expressed as Equation (1), in which NB # is the TNI of the