Ionized ethylidene ketene and its homologue methylene ketene

The gas phase pyrolyses of crotonic and acrylic-trifluoroacetic anhydrides were shown to yield ethylidene ketene [CH 3 CH=C=C=O] and methylene ketene [CH 2 =C=C=O], respectively. The former was identified via the collisional activation mass spectrum of its molecular ion. The ionization energies of the two ketenes, 8.68 and 9.12 ± 0.05 eV respectively, measured using energy selected electrons, lead to 215 and 233 kcal mol −1 for their ionic heats of formation.