Barrier-free proton transfer induced by electron attachment to the complexes between 1-methylcytosine and formic acid

We report the photoelectron spectra of anionic complexes between 1-methylcytosine (mC) and formic acid (FA) in 1 : 1 and 1:2 stoichiometries that have been measured with 2.54 eV photons. Each spectrum consists of a broad peak with maxima at 1.85 and 2.1 eV, respectively, confirming the generation of stable valence anions in the gas phase. The neutral and anionic complexes of mC(FA) and mC(FA)₂ were also studied computationally at the B3LYP, second-order Møller-Plesset, and coupled-cluster levels of theory with the 6-31++G** and aug-cc-pVDZ basis sets. Based on the calculations, we conclude that the photoelectron spectra of mC(FA)- and mC(FA)₂ are due to anions that originate from a barrier-free proton transfer (BFPT) triggered by excess electron attachment. They can be viewed as neutral radicals of hydrogenated 1-methylcytosine solvated by a deprotonated formic acid. © 2010 Taylor & Francis.