Puppi, P. S.Barbosa, A. SouzaJones, N. C.Hoffmann, S. V.Akther, U. S.Mason, N. J.Limão-Vieira, P.2025-06-052025-06-052025-010022-4073PURE: 117947300PURE UUID: 55d18871-b645-4831-999b-52b4fea6807dScopus: 85208335181WOS: 001355236400001ORCID: /0000-0003-2696-1152/work/185462127http://hdl.handle.net/10362/183933PSP and ASB acknowledge support from the Brazilian agencies Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES). PSP and ASB also acknowledge Prof. Carlos A. M. de Carvalho for computational support at LFTC-DFis-UFPR and at LCPAD-UFPR. This work was also supported by Radiation Biology and Biophysics Doctoral Training Programme (RaBBiT, PD/00193/2012). PLV also acknowledges his visiting professor position at Federal University of Paran\u00E1, Curitiba, Brazil and CAPES PrInt/UFPR. Publisher Copyright: © 2024 The Author(s)Synchrotron radiation has been used to record for the first time absolute vacuum ultraviolet photoabsorption cross-sections of trifluoroacetic acid (TFA) and chlorodifluoroacetic acid (CDFA) in the 4.5–10.8 eV energy range. In order to further our knowledge of the major electronic transitions and thus help interpret the photoabsorption data, theoretical calculations using time-dependent density functional theory (TD-DFT) level have been performed. These calculations have provided important information on the nature of the excited electronic states which have been assigned to valence, mixed valence-Rydberg and Rydberg transitions. Due to the lack of any information about CDFA ionic states, we also provide Equation-of-Motion Coupled-Cluster Single and Doubles (EOM-CCSD) vertical ionisation energies. Photolysis lifetimes in the Earth's atmosphere for both chemical compounds have also been estimated from the absolute photoabsorption cross-section data.948133engChlorodifluoroacetic acidCross-sectionPhotoabsorptionRydberg statesTrifluoroacetic acidRadiationAtomic and Molecular Physics, and OpticsSpectroscopyjournal article10.1016/j.jqsrt.2024.109257https://www.scopus.com/pages/publications/85208335181