Photoelectron spectroscopy of homogeneous nucleic acid base dimer anions.

We report the photoelectron spectra of homogeneous dimer anions of the nucleobases: uracil, thymine, cytosine, adenine, and guanine, i.e., U(2)(-), T(2)(-), C(2)(-), A(2)(-), and G(2)(-) along with DFT calculations on U(2)(-) and T(2)(-). Based on these calculations the photoelectron spectrum of T(2)(-) was assigned as being due to both a proton transferred and a non-proton transferred isomer, while the photoelectron spectrum of U(2)(-) was assigned in terms of a single dominant barrier-free proton transferred isomer. Photoelectron spectra were also measured with a different source and on a different type of photoelectron spectrometer for U(2)(-), T(2)(-), A(2)(-), (1-MeT)(2)(-) and (1,3-Me(2)U)(2)(-).