Tracing the origins of nitrogen bearing organics toward Orion KL with ALMA

Abstract

A comprehensive anal. of a broadband 1.2 THz wide spectral survey of the Orion Kleinmann-Low nebula (Orion-KL) has shown that nitrogen bearing complex orgs. trace systematically hotter gas than O-bearing orgs. toward this source. The origin of this O/N dichotomy remains a mystery. If complex mols. originate from grain surfaces, N-bearing species may be more difficult to remove from grain surfaces than O-bearing orgs. Theor. studies, however, have shown that hot (T=300 K) gas phase chem. can produce high abundances of N-bearing orgs. while suppressing the formation of Obearing complex mols. Measurement of gradients in isotopic fractionation at spatial scales commensurate with the forces driving this chem. can distinguish these distinct formation pathways. Isotopic fractionation is a relatively common tool in astrochem., however until recently it has not been possible to measure fractionation at high angular resoln. The Atacama Large Millimeter/Submillimeter Array (ALMA) combines the sensitivity and angular resoln. required for these measurements, and represents a new method of approaching observational astrochem. We have obtained extremely high angular resoln. observations of Me cyanide (CH3CN) using the ALMA toward Orion KL. By simultaneously imaging 13CH3CN and CH2DCN we map the temp. structure and D/H ratio of CH3CN. We will present the results of these observations and discuss their implications for the formation of N-bearing orgs. in the interstellar medium.

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