Ketene Formation in Interstellar Ices: A Laboratory Study

Abstract

The formation of ketene (H 2 CCO, ethenone) in polar and apolar ices was studied with in situ 0.8 MeV proton irradiation, far-UV photolysis, and infrared spectroscopic analyses at 10-20 K. Using isotopically enriched reagents, unequivocal evidence was obtained for ketene synthesis in H 2 O-rich and CO 2 -rich ices, and several reaction products were identified. Results from scavenging experiments suggested that ketene was formed by free-radical pathways, as opposed to acid-base processes or redox reactions. Finally, we use our results to draw conclusions about the formation and stability of ketene in the interstellar medium.

Formation of complex molecules in translucent clouds: acetaldehyde, vinyl alcohol, ketene, and ethanol via “nonenergetic” processing of C2H2ice

“…2 and clearly shows the spectral redshift corresponding to species' C 18 O vibrational modes. Besides H 2 18 O 2 signals (i.e., 1384 and 832 cm −1 ), IR features of CH 2 C 18 O (ν 2 ), CH 3 CH 18 O (ν 4 ), CH 2 CH 18 OH (ν 9 ), and CH 3 CH 2 18 OH (ν 11 ) are found at 2106, 1677, 1114, and 1030 cm −1 , respectively (Hawkins & Andrews 1983;Rodler et al 1984;Hudson & Loeffler 2013;Maity et al 2014;Bergner et al 2019). Peak positions due to transitions not directly affected by O-atoms, such as the C-C stretching modes (1662 and 1639 cm −1 ) of CH 2 CH 18 OH and the CH 3 deformation (1351 cm −1 ) as well as the C-C stretching (1133 cm −1 ) mode of CH 3 CH 18 O do not shift more than the 1 cm −1 with respect to the same transitions of the main isotope, which is within our spectral resolution (Rodler et al 1984;Hawkins & Andrews 1983).…”

“…The IR features with relatively weak absorption coefficiency, which originate from the CH 3 deformation (ν 5 ) mode of acetaldehyde and CH 2 scissor (ν 6 ) mode of vinyl alcohol, are strongly blended with a broad H 2 O 2 peak Article number, page 5 of 17 Ethanol (CH 3 CH 2 OH) is clearly observed at 1041 cm −1 through its C-O stretching (ν 11 ) mode along with a relatively small feature at 1086 cm −1 (ν 10 ; CH 3 rocking mode) (Barnes & Hallam 1970;Mikawa et al 1971;Boudin et al 1998). The peak located at 2133 cm −1 can be assigned to the C=O stretching (ν 2 ) mode of ketene (CH 2 CO) (Hudson & Loeffler 2013). A tiny peak at ∼1744 cm −1 is tentatively assigned to the C=O stretching (ν 4 ) of acetic acid (Bahr et al 2006;Bertin et al 2011).…”

Complex Organic Molecules toward Embedded Low-mass Protostars∗

“…CH 2 CO: CH 2 CO formation has been demonstrated experimentally by ice processing, with proposed formation mechanisms of either C 2 O hydrogenation (Maity et al 2014) or vinyl alcohol formation and decomposition (Hudson & Loeffler 2013). However, theory indicates that H addition to C 2 O is the dominant pathway (Garrod et al 2008).…”

Synthesis of the Smallest Member of the Silylketene Family: H3SiC(H)=C=O

“…[4] Its synthetic pathways in the ISM involvei nteraction of interstellar icy grains carrying methane and carbon monoxide with ionizing radiation at 10 K followed by sublimation of the ices in the hot core phase. [5,6] It was suggested that ketene forms molecules with ap eptide bond upon reactionw ith an amino acid;a nd in accordance with this, N-acetyl amino acids wasi dentified in meteorites such as Murchison. [7] More than half ac entury later,s ilylketenes were discovered.…”

“…Based on these spectroscopic studies, ketene was identified in the interstellar medium (ISM) toward the star forming region Sagittarius B2 via the 4 13 ‐3 12 , 5 15 ‐4 14 , and 5 12 ‐4 13 transitions between 81 and 101 GHz . Its synthetic pathways in the ISM involve interaction of interstellar icy grains carrying methane and carbon monoxide with ionizing radiation at 10 K followed by sublimation of the ices in the hot core phase . It was suggested that ketene forms molecules with a peptide bond upon reaction with an amino acid; and in accordance with this, N ‐acetyl amino acids was identified in meteorites such as Murchison…”