Excited States of Proton-bound DNA/RNA Base Homo-dimers: Pyrimidines

We are presenting the electronic photo fragment spectra of the protonated pyrimidine DNA bases homo-dimers. Only the thymine dimer exhibits a well structured vibrational progression, while protonated monomer shows broad vibrational bands. This shows that proton bonding can block some non radiative processes present in the monomer.Comment: We acknowledge the use of the computing facility cluster GMPCS of the LUMAT federation (FR LUMAT 2764

Interaction between aromatic amine cations and nonpolar solvents: Infrared spectra of isomeric aniline

Infrared (IR) photodissociation spectra of the aniline+–Arn cations, An$^+{-}{\rm Ar}_n$ (n=1,2), are analyzed in the vicinity of the N–H stretch fundamentals. The complexes are produced in an electron impact (EI) ion source which produces predominantly the most stable cluster isomers. Two isomers of are identified by their characteristic N–H stretch frequencies: the planar proton-bound global minimum, in which the Ar ligand forms a nearly linear H-bond to the amino group, and the less stable local minimum, in which the Ar atom is attached to the π-electron system of the aromatic ring. This result is the first unambiguous detection of the most stable dimer. All previous spectroscopic studies of An+–Ar employed resonance enhanced multiphoton ionization (REMPI) of neutral and identified only the less stable cation due to restrictions arising from the Franck-Condon principle. The EI-IR spectrum of shows that the most stable structure of this trimer features two equivalent H-bonds ($C_{2v}$ symmetry). The interpretation of the experimental data is supported by quantum chemical calculations. The ab initio potential of An+–Ar calculated at the UMP2/6-311G(2df, 2pd) level features global minima ($D_{\rm e}=513$ cm-1) and local minima ($D_{\rm e}=454$ cm-1), with a barrier of $V_{\rm b}\approx 140$ cm-1 for isomerization from the toward the minimum