Electronic structure and spectroscopy of nucleic acid bases: Ionization energies, ionization-induced structural changes, and photoelectron spectra
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 were computed using equation-of-motion coupled-cluster method for ionization potentials with single and double substitutions. Equilibrium structures of the cationic ground states were characterized by DFT with the {omega}B97X-D functional. The ionization-induced 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 ionization energies (8.13, 8.89, 8.51-8.67 and 7.75-7.87 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 S{sub 0}-D{sub 0} vibronic bands computed within double-harmonic approximation with Duschinsky rotations are compared with previously reported experimental photoelectron spectra.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- Chemical Sciences Division
- DOE Contract Number:
- DE-AC02-05CH11231
- OSTI ID:
- 1001048
- Report Number(s):
- LBNL-4111E; ISSN 1520--5215; TRN: US201101%%809
- Journal Information:
- Journal of Physical Chemistry A, Vol. 114, Issue 46; ISSN 1089--5639
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
37
ADENINES
APPROXIMATIONS
CYTOSINE
EFFICIENCY
ELECTRONIC STRUCTURE
GEOMETRY
GROUND STATES
GUANINE
IONIZATION
IONIZATION POTENTIAL
MASS SPECTROSCOPY
NUCLEIC ACIDS
PHOTOIONIZATION
RELAXATION
SPECTRA
SPECTROSCOPY
THYMINE
Electronic structure
spectroscopy
nucleic
acid
bases
Ionization
energies
ionization-induced
photoelectron
spectra