Experimental and theoretical study of [C3H2O]+· cations. Evidence for the existence of stable [CH=CH-CO]+· ions in the gas phase

Ab initio molecular orbital calculations using polarization basis sets and incorporating valence-electron correlation have been used to determine structures and relative energies of isomers in the C3H2O⁺· potential energy surface. In addition to the high-energy keto/enol species [HC≡C-CHO]⁺·/[HC≡C-C-OH]⁺· and the experimentally characterized propadienone and cyclopropenone radical cations, an isomer which has no neutral stable counterpart [CH=CH-C=O]⁺· is reported to be a stable species. Experimental evidence is presented that this ion is generated by the gas-phase dissociative ionization of maleic anhydride and cyclopentene-3,5-dione. Both the calculations and the experimental observations show that its heat of formation is close to that of the most stable C3H2O⁺· isomer, [propadienone]⁺·. © 1986 American Chemical Society.