Electronic structure and spectroscopy of nucleic acid bases:
Ionization energies, ionization-induced structural changes, and photoelectron
K.B. Bravaya, O. Kostko, S. Dolgikh, A. Landau, M. Ahmed, and A.I. Krylov
J. Phys. Chem. A 114, 12305 – 12317
We report high-level ab initio calculations and
single-photon ionization mass spectrometry study of
ionization of adenine (A), thymine (T), cytosine (C) and guanine (G).
For thymine and adenine, only the lowest-energy tautomers were
considered, whereas for cytosine and guanine we characterized
five lowest-energy tautomeric forms. The first adiabatic and
several vertical ionization energies (IEs) were computed using
coupled-cluster method for ionization potentials with single and double
substitutions. Equilibrium structures of the cationic ground states
were characterized by DFT with the wB97X-D functional.
geometry changes of the bases are consistent with the shapes of the
corresponding molecular orbitals.
For the lowest-energy tautomers, the magnitude of the structural relaxation
decreases in the
following series G>C>A>T, the respective
relaxation energies being 0.41, 0.32, 0.25 and 0.20 eV.
The computed adiabatic IEs (8.12, 8.93, 8.52-8.71 and 7.75-7.88 eV for A,T,C
and G, respectively) agree well with the onsets of the photoionization
efficiency (PIE) curves (8.20+/-0.05, 8.95+/-0.05, 8.60+/-0.05 and
7.75+/-0.05 eV). Vibrational progressions for the S0-D0
vibronic bands computed within double-harmonic approximation with
are compared with previously reported experimental photoelectron spectra.
Download this paper (PDF, NaN kB)
Electronic structure of model charge transport systems: from helium dimer to DNA
Interface between electronic structure, spectroscopy, and dynamics