skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: A THREE-PHASE CHEMICAL MODEL OF HOT CORES: THE FORMATION OF GLYCINE

Abstract

A new chemical model is presented that simulates fully coupled gas-phase, grain-surface, and bulk-ice chemistry in hot cores. Glycine (NH{sub 2}CH{sub 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 {approx}40-120 K. Peak gas-phase glycine fractional abundances lie in the range 8 Multiplication-Sign 10{sup -11}-8 Multiplication-Sign 10{sup -9}, occurring at {approx}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, formore » bright, nearby sources with narrow emission lines. Photodissociation of water and subsequent hydrogen abstraction from organic molecules by OH, and NH{sub 2}, are crucial to the buildup 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.« less

Authors:
 [1]
  1. Center for Radiophysics and Space Research, Cornell University, Ithaca, NY 14853-6801 (United States)
Publication Date:
OSTI Identifier:
22167609
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 765; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTRONOMY; ASTROPHYSICS; COMPARATIVE EVALUATIONS; COSMIC DUST; COSMOCHEMISTRY; ELEMENT ABUNDANCE; EVAPORATION; GLYCINE; HYDROGEN; ICE; INTERSTELLAR GRAINS; MOLECULES; PHOTOLYSIS; PHOTON EMISSION; PROPIONIC ACID; RADIANT HEAT TRANSFER; STAR CLUSTERS

Citation Formats

Garrod, Robin T., E-mail: rgarrod@astro.cornell.edu. A THREE-PHASE CHEMICAL MODEL OF HOT CORES: THE FORMATION OF GLYCINE. United States: N. p., 2013. Web. doi:10.1088/0004-637X/765/1/60.
Garrod, Robin T., E-mail: rgarrod@astro.cornell.edu. A THREE-PHASE CHEMICAL MODEL OF HOT CORES: THE FORMATION OF GLYCINE. United States. https://doi.org/10.1088/0004-637X/765/1/60
Garrod, Robin T., E-mail: rgarrod@astro.cornell.edu. 2013. "A THREE-PHASE CHEMICAL MODEL OF HOT CORES: THE FORMATION OF GLYCINE". United States. https://doi.org/10.1088/0004-637X/765/1/60.
@article{osti_22167609,
title = {A THREE-PHASE CHEMICAL MODEL OF HOT CORES: THE FORMATION OF GLYCINE},
author = {Garrod, Robin T., E-mail: rgarrod@astro.cornell.edu},
abstractNote = {A new chemical model is presented that simulates fully coupled gas-phase, grain-surface, and bulk-ice chemistry in hot cores. Glycine (NH{sub 2}CH{sub 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 {approx}40-120 K. Peak gas-phase glycine fractional abundances lie in the range 8 Multiplication-Sign 10{sup -11}-8 Multiplication-Sign 10{sup -9}, occurring at {approx}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{sub 2}, are crucial to the buildup 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.},
doi = {10.1088/0004-637X/765/1/60},
url = {https://www.osti.gov/biblio/22167609}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 765,
place = {United States},
year = {Fri Mar 01 00:00:00 EST 2013},
month = {Fri Mar 01 00:00:00 EST 2013}
}