Pathways To Oxygen-bearing Molecules In The Interstellar Mediumand In Planetary Atmospheres: Cyclopropenone (c-c_3h_2o) and Propynal (hcccho)

摘要

We investigated the formation of two C_3H_2O isomers, i.e., cyclopropenone (c-C_3H_2O) and propynal (HCCCHO), in binary ice mixtures of carbon monoxide (CO) and acetylene (C_2H_2) at 10 K in an ultrahigh vacuum machine on high-energy electron irradiation. The chemical evolution of the ice samples was followed online and in situ via a Fourier transform infrared spectrometer and a quadrupole mass spectrometer. The temporal profiles of the cyclopropenone and propynal isomers suggest (pseudo-) first-order kinetics. The cyclic structure (c-C_3H_2O) is formed via an addition of triplet carbon monoxide to ground-state acetylene (or vice versa); propynal (HCCCHO) can.be synthesized from a carbon monoxide-acetylene complex via a [HCO...CCH ] radical pair inside the matrix cage. These laboratory studies showed for the first time that both C_3H_2O isomers can be formed in low-temperature ices via nonequilibrium chemistry initiated by energetic electrons as formed in the track of Galactic cosmic ray particles penetrating interstellar icy grains in cold molecular clouds. Our results can explain the hitherto unresolved gas phase abundances of cyclopropenone in star-forming regions via sublimation of c-C_3H_2O as formed on icy grains in the cold molecular cloud stage. Implications for the heterogeneous oxygen chemistry of Titan and icy terrestrial planets and satellites suggest that the production of oxygen-bearing molecules such as C_3H_2O may dominate on aerosol particles compared to pure gas phase chemistry.