Accession Number N20120013461
Title Observations of Carbon Isotopic Fractionation in Interstellar Formaldehyde.
Publication Date Mar 2012
Media Count 2p
Personal Author C. M. Persson E. S. Wirstrom S. B. Charnley W. D. Geppert
Abstract Primitive Solar System materials (e.g. chondrites. IDPs, the Stardust sample) show large variations in isotopic composition of the major volatiles (H, C, N, and O) even within samples, witnessing to various degrees of processing in the protosolar nebula. For example. the very pronounced D enhancements observed in IDPs (I) . are only generated in the cold. dense component of the interstellar medium (ISM), or protoplanetary disks, through ion-molecule reactions in the presence of interstellar dust. If this isotopic anomaly has an interstellar origin, this leaves open the possibility for preservation of other isotopic signatures throughout the form ation of the Solar System. The most common form of carbon in the ISM is CO molecules, and there are two potential sources of C-13 fractionation in this reservoir: low temperature chemistry and selective photodissociation. While gas-phase chemistry in cold interstellar clouds preferentially incorporates C-13 into CO (2), the effect of self-shielding in the presence of UV radiation instead leads to a relative enhancement of the more abundant isotopologue, 12CO. Solar System organic material exhibit rather small fluctuations in delta C-13 as compared to delta N-15 and delta D (3)(1), the reason for which is still unclear. However, the fact that both C-13 depleted and enhanced material exists could indicate an interstellar origin where the two fractionation processes have both played a part. Formaldehyde (H2CO) is observed in the gas-phase in a wide range of interstellar environments, as well as in cometary comae. It is proposed as an important reactant in the formation of more complex organic molecules in the heated environments around young stars, and formaldehyde polymers have been suggested as the common origin of chondritic insoluable organic matter (IOM) and cometary refractory organic solids (4). The relatively high gas-phase abundance of H2CO observed in molecular clouds (10(exp- 9) - 10(exp- 8) relative to H2) makes it feasible to observe its less common isotopologues. As a step in our investigation of C-13 fractionation patterns in the ISM, we here present comparisons between observations of the C-13 fraction in formaldehyde, and chemical fractionation models.
Keywords Abundance
Carbon 13
Carbon monoxide
Chemical fractionation
Chemical reactions
Cosmic dust
Interstellar chemistry
Interstellar matter
Isotope ratios
Low temperature
Methyl alcohol
Molecular clouds
Protoplanetary disks

Source Agency National Aeronautics and Space Administration
NTIS Subject Category 54 - Astronomy & Astrophysics
84B - Extraterrestial Exploration
Corporate Author Goddard Space Flight Center, Greenbelt, MD.
Document Type Technical report
Title Note N/A
NTIS Issue Number 1401
Contract Number N/A

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