Dissociative Photodetachment of the Ethoxide Anion and Stability of the Ethoxy Radical CH₃CH₂O^•

The ethoxy radical is an important species in combustion chemistry; however, considerable debate regarding the fragmentation pathways exists. In order to examine the stability and dissociation dynamics of the ethoxy radical in the two lowest electronic states, dissociative photodetachment experiments at 3.20 eV were carried out on the ethoxide anion, CH₃CH₂O^–, and its per-deuterated isotopologue. Production of excited radicals by photodetachment of the alkoxide anion was found to lead to only CH₃ + H₂CO products, with no indication of the energetically allowed H-loss channel, H + CH₃CHO. Ab initio calculations for the anionic and neutral surfaces, including relevant isomerization and dissociation barriers, were carried out using the CBS-QB3 method to aid in interpretation of the data. The energetics observed in the photoelectron–photofragment coincidence spectra indicate that the calculated barrier (0.70 eV) for the process CH₃CH₂O → CH₃ + H₂CO and the stability of the CH₃CH₂O radical relative to those products are upper limits