Glycolonitrile (HOCH 2 CN) Chemistry in Star-forming Regions

Abstract

Glycolonitrile (HOCH 2 CN) is an attractive interstellar prebiotic molecule. Glycolonitrile is considered not only as a possible precursor for glycine but also as a key intermediate for adenine formation. Recently, HOCH 2 CN was detected toward IRAS 16293−2422 B with the Atacama Large Millimeter/submillimeter Array (ALMA). In this study we perform a comprehensive modeling study on HOCH 2 CN chemistry under the physical conditions of IRAS 16293−2422 B’s cold envelope and hot corino evolutions using the astrochemical code NAUTILUS and the updated gas-grain chemical network. Our studies not only give the main reactions and the favorable physical conditions for the formation of HOCH 2 CN but also uncover that the observed glycolonitrile in the cold envelope originates from the gradual accumulation of the gas-phase molecules during the ambient cloud, freefall collapse, and warm-up phases of the cold envelope evolution, and in the hot corino it mainly comes from the accumulated ices during the hot corino evolution. Using the updated chemical network, we also conduct chemical simulations under the physical conditions of Sagittarius (Sgr) B2(N) evolution. The simulation results show that varying the cosmic-ray ionization rate is needed to best reproduce the observational upper limits of HOCH 2 CN and the observed abundances of CNCHO and CH 2 CNH toward Sgr B2(N). Moreover, we predict that HOCHCNH, OCH 2 CN, HOCHCN, HOCCNH, OCCNH, and OCCN have high abundances and may be detectable toward IRAS 16293−2422 B and Sgr B2(N).