For the CH3CHOO Criegee intermediates (ethanal-oxide) and analogous anions, we obtain heats of formations and electron affinities at CCSDT(Q)/CBS level of theory by means of the high-level W3-F12 thermochemical protocol. The electron affinities amount to 0.20 eV and 0.35 eV for the cis and trans isomer, respectively. Neutral cis and trans isomers are separated by 14.1 kJ/mol, the anions are almost isoenergetic (0.4 kJ/mol separation). Harmonic vibrational frequencies are presented at CCSD(T)/aug'-cc-pVTZ level of theory. Since the synthesis of these species in gas-phase experiments might be possible in the near future, we include a predicted photoelectron spectrum. (C) 2014 Elsevier B.V. All rights reserved.