A new chemical model is presented that simulates fully-coupled gas-phase , grain-surface and bulk-ice chemistry in hot cores .
Glycine ( NH _ { 2 } CH _ { 2 } COOH ) , the simplest amino acid , and related molecules such as glycinal , propionic acid and propanal , are included in the chemical network .
Glycine is found to form in moderate abundance within and upon dust-grain ices via three radical-addition mechanisms , with no single mechanism strongly dominant .
Glycine production in the ice occurs over temperatures \sim 40–120 K. Peak gas-phase glycine fractional abundances lie in the range 8 \times 10 ^ { -11 } – 8 \times 10 ^ { -9 } , occuring at \sim 200 K , the evaporation temperature of glycine .
A gas-phase mechanism for glycine production is tested and found insignificant , even under optimal conditions .
A new spectroscopic radiative-transfer model is used , allowing the translation and comparison of the chemical-model results with observations of specific sources .
Comparison with the nearby hot-core source NGC 6334 IRS1 shows excellent agreement with integrated line intensities of observed species , including methyl formate .
The results for glycine are consistent with the current lack of a detection of this molecule toward other sources ; the high evaporation temperature of glycine renders the emission region extremely compact .
Glycine detection with ALMA is predicted to be highly plausible , for bright , nearby sources with narrow emission lines .
Photodissociation of water and subsequent hydrogen-abstraction from organic molecules by OH , and NH _ { 2 } , are crucial to the build-up of complex organic species in the ice .
The inclusion of alternative branches within the network of radical-addition reactions appears important to the abundances of hot-core molecules ; less favorable branching ratios may remedy the anomalously high abundance of glycolaldehyde predicted by this and previous models .