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

Abstract

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 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.

Keywords:

• anion photoelectron spectroscopy
• barrier-free proton transfer

Acknowledgements

The experimental part of this work was supported by the National Science Foundation under grant No. CHE-0809258 (K.H.B.), and the theoretical parts were supported by the Polish State Committee for Scientific Research (KBN), grants KBN/N N204 023135 (J.R.) and DS/8221-4-0140-8 (P.S.), and by the U.S. Department of Energy under contract DE-AC02-05CH11231 and through a 2008 Seaborg Fellowship at Lawrence Berkeley National Laboratory (M.H.). The calculations were performed at the Academic Computer Center in Gdańsk (TASK).