A theoretical and experimental study of the near edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectra (XPS) of nucleobases: thymine and adenine

The core level electron excitation and ionization spectra of thymine and adenine have been investigated by photoabsorption and photoemission spectroscopy, and the results interpreted by means of ab initio calculations using the second-order algebraicdiagrammatic construction (ADC(2)) method for the polarization propagator and the fourth-order ADC method (ADC(4)) for the one-particle Green's function. The photoabsorption spectra are dominated by transitions from core levels to unoccupied π states, but also show clear structures due to Rydberg transitions. The calculated spectra are in good agreement with the experimental results, and many of the observed structures are assigned.