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Title: ORTHO-PARA SELECTION RULES IN THE GAS-PHASE CHEMISTRY OF INTERSTELLAR AMMONIA

Abstract

The ortho-para chemistry of ammonia in the cold interstellar medium is investigated using a gas-phase chemical network. Branching ratios for the primary reaction chain involved in the formation and destruction of ortho- and para-NH{sub 3} were derived using angular momentum rules based on the conservation of the nuclear spin. We show that the 'anomalous' ortho-to-para ratio of ammonia ({approx}0.7) observed in various interstellar regions is in fact consistent with nuclear spin selection rules in a para-enriched H{sub 2} gas. This ratio is found to be independent of temperature in the range 5-30 K. We also predict an ortho-to-para ratio of {approx}2.3 for NH{sub 2}. We conclude that a low ortho-to-para ratio of H{sub 2} naturally drives the ortho-to-para ratios of nitrogen hydrides below the statistical values.

Authors:
; ; ;  [1];  [2]
  1. UJF-Grenoble 1/CNRS-INSU, Institut de Planetologie et d'Astrophysique de Grenoble (IPAG) UMR 5274, Grenoble F-38041 (France)
  2. Institut d'Astrophysique Spatiale, Universite Paris-Orsay and CNRS, Orsay (France)
Publication Date:
OSTI Identifier:
22118799
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 770; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; AMMONIA; ASTRONOMY; ASTROPHYSICS; BRANCHING RATIO; COSMOCHEMISTRY; HYDROGEN; INTERSTELLAR SPACE; MOLECULES; SELECTION RULES; SPIN

Citation Formats

Faure, A., Hily-Blant, P., Le Gal, R., Rist, C., and Pineau des Forets, G., E-mail: afaure@obs.ujf-grenoble.fr. ORTHO-PARA SELECTION RULES IN THE GAS-PHASE CHEMISTRY OF INTERSTELLAR AMMONIA. United States: N. p., 2013. Web. doi:10.1088/2041-8205/770/1/L2.
Faure, A., Hily-Blant, P., Le Gal, R., Rist, C., & Pineau des Forets, G., E-mail: afaure@obs.ujf-grenoble.fr. ORTHO-PARA SELECTION RULES IN THE GAS-PHASE CHEMISTRY OF INTERSTELLAR AMMONIA. United States. doi:10.1088/2041-8205/770/1/L2.
Faure, A., Hily-Blant, P., Le Gal, R., Rist, C., and Pineau des Forets, G., E-mail: afaure@obs.ujf-grenoble.fr. Mon . "ORTHO-PARA SELECTION RULES IN THE GAS-PHASE CHEMISTRY OF INTERSTELLAR AMMONIA". United States. doi:10.1088/2041-8205/770/1/L2.
@article{osti_22118799,
title = {ORTHO-PARA SELECTION RULES IN THE GAS-PHASE CHEMISTRY OF INTERSTELLAR AMMONIA},
author = {Faure, A. and Hily-Blant, P. and Le Gal, R. and Rist, C. and Pineau des Forets, G., E-mail: afaure@obs.ujf-grenoble.fr},
abstractNote = {The ortho-para chemistry of ammonia in the cold interstellar medium is investigated using a gas-phase chemical network. Branching ratios for the primary reaction chain involved in the formation and destruction of ortho- and para-NH{sub 3} were derived using angular momentum rules based on the conservation of the nuclear spin. We show that the 'anomalous' ortho-to-para ratio of ammonia ({approx}0.7) observed in various interstellar regions is in fact consistent with nuclear spin selection rules in a para-enriched H{sub 2} gas. This ratio is found to be independent of temperature in the range 5-30 K. We also predict an ortho-to-para ratio of {approx}2.3 for NH{sub 2}. We conclude that a low ortho-to-para ratio of H{sub 2} naturally drives the ortho-to-para ratios of nitrogen hydrides below the statistical values.},
doi = {10.1088/2041-8205/770/1/L2},
journal = {Astrophysical Journal Letters},
number = 1,
volume = 770,
place = {United States},
year = {Mon Jun 10 00:00:00 EDT 2013},
month = {Mon Jun 10 00:00:00 EDT 2013}
}