Mayer Dennis, Titov Evgenii, Lever Fabiano, Mehner Lisa, Murillo-Sánchez Marta L, Walz Constantin, Bozek John, Saalfrank Peter, Gühr Markus
Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany.
Institut für Chemie, Universität Potsdam, Karl-Liebknecht-Str. 24/25, 14476 Potsdam, Germany.
J Chem Phys. 2025 Aug 21;163(7). doi: 10.1063/5.0279536.
We present a combined experimental and theoretical study of the vibrationally resolved valence photoelectron spectra of the complete series of thiouracils (2-thiouracil, 4-thiouracil, and 2,4-dithiouracil) for binding energies between 8 and 17 eV. The theoretical spectra were calculated using equation-of-motion coupled cluster theory for ionization potential combined with the time-independent double-harmonic adiabatic Hessian approach. For all three thiouracils, the first ionization potential is found between 8.4 and 8.7 eV, which is 1 eV lower than for the canonical nucleobase uracil. Ionization bands up to 12 eV show strong vibrational progressions and are well reproduced by the calculations. These bands are attributed to the ionization of (primarily) sulfur- and oxygen-localized valence molecular orbitals. For higher binding energies, the calculations indicate that nonadiabatic couplings are important for the interpretation of the photoelectron spectra.
