AN AB-INITIO STUDY OF THE C3H2O POTENTIAL SURFACE - A MECHANISM FOR PROPYNAL FORMATION AND DESTRUCTION

The C3H2O potential energy surface, including the C-3 . H2O complex, h ydroxypropadienylidene, propynal, cyclopropenone, and propadienone, ha s been calculated at the HF/6-31G, QCISD(T)/6-31G*//HF/6-31G*, and MP 2/6-31G levels. It is shown that photolysis of the C-3 . H2O complex leads initially to hydroxypropadienylidene, as has been observed. Furt her photolysis is predicted to lead to propynal via successive H atom migrations along the CCCO framework. Photodepletion of propynal genera tes either cyclopropenone or propadienone, from either of which acetyl ene and CO should be produced. Experimental evidence is presented to s upport this mechanism. It is proposed that the propynal observed in th e interstellar medium is produced via the photolysis of the C-3 . H2O complex in the icy mantles of interstellar dust grains and not via gas eous ion-molecule reactions, as previously proposed.