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Title: The ortho-to-para ratio of H 2 Cl + : Quasi-classical trajectory calculations and new simulations in light of new observations

Abstract

Multi-hydrogenated species with proper symmetry properties can present different spin configurations, and thus exist under different spin symmetry forms, labeled as para and ortho for two-hydrogen molecules. We investigated here the ortho-to-para ratio (OPR) of H2Cl+ in the light of new observations performed in the z = 0.89 absorber toward the lensed quasar PKS 1830-211 with the Atacama Large Millimeter/submillimeter Array (ALMA). Two independent lines of sight were observed, to the southwest (SW) and northeast (NE) images of the quasar, with OPR values found to be 3.15 ± 0.13 and 3.1 ± 0.5 in each region, respectively, in agreement with a spin statistical weight of 3:1. An OPR of 3:1 for a molecule containing two identical hydrogen nuclei can refer to either a statistical result or a high-temperature limit depending on the reaction mechanism leading to its formation. It is thus crucial to identify rigorously how OPRs are produced in order to constrain the information that these probes can provide. To understand the production of the H2Cl+ OPR, we undertook a careful theoretical study of the reaction mechanisms involved with the aid of quasi-classical trajectory calculations on a new global potential energy surface fit to a large number of high-levelmore » ab initio data. Our study shows that the major formation reaction for H2Cl+ produces this ion via a hydrogen abstraction rather than a scrambling mechanism. Such a mechanism leads to a 3:1 OPR, which is not changed by destruction and possible thermalization reactions for H2Cl+ and is thus likely to be the cause of observed 3:1 OPR ratios, contrary to the normal assumption of scrambling.« less

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Univ. of New Mexico, Albuquerque, NM (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1540110
Grant/Contract Number:  
SC0015997
Resource Type:
Accepted Manuscript
Journal Name:
Astronomy and Astrophysics
Additional Journal Information:
Journal Volume: 608; Journal ID: ISSN 0004-6361
Publisher:
EDP Sciences
Country of Publication:
United States
Language:
English
Subject:
Astronomy & Astrophysics

Citation Formats

Le Gal, R., Xie, C., Herbst, E., Talbi, D., Guo, H., and Muller, S. The ortho-to-para ratio of H 2 Cl + : Quasi-classical trajectory calculations and new simulations in light of new observations. United States: N. p., 2017. Web. doi:10.1051/0004-6361/201731566.
Le Gal, R., Xie, C., Herbst, E., Talbi, D., Guo, H., & Muller, S. The ortho-to-para ratio of H 2 Cl + : Quasi-classical trajectory calculations and new simulations in light of new observations. United States. doi:10.1051/0004-6361/201731566.
Le Gal, R., Xie, C., Herbst, E., Talbi, D., Guo, H., and Muller, S. Fri . "The ortho-to-para ratio of H 2 Cl + : Quasi-classical trajectory calculations and new simulations in light of new observations". United States. doi:10.1051/0004-6361/201731566. https://www.osti.gov/servlets/purl/1540110.
@article{osti_1540110,
title = {The ortho-to-para ratio of H 2 Cl + : Quasi-classical trajectory calculations and new simulations in light of new observations},
author = {Le Gal, R. and Xie, C. and Herbst, E. and Talbi, D. and Guo, H. and Muller, S.},
abstractNote = {Multi-hydrogenated species with proper symmetry properties can present different spin configurations, and thus exist under different spin symmetry forms, labeled as para and ortho for two-hydrogen molecules. We investigated here the ortho-to-para ratio (OPR) of H2Cl+ in the light of new observations performed in the z = 0.89 absorber toward the lensed quasar PKS 1830-211 with the Atacama Large Millimeter/submillimeter Array (ALMA). Two independent lines of sight were observed, to the southwest (SW) and northeast (NE) images of the quasar, with OPR values found to be 3.15 ± 0.13 and 3.1 ± 0.5 in each region, respectively, in agreement with a spin statistical weight of 3:1. An OPR of 3:1 for a molecule containing two identical hydrogen nuclei can refer to either a statistical result or a high-temperature limit depending on the reaction mechanism leading to its formation. It is thus crucial to identify rigorously how OPRs are produced in order to constrain the information that these probes can provide. To understand the production of the H2Cl+ OPR, we undertook a careful theoretical study of the reaction mechanisms involved with the aid of quasi-classical trajectory calculations on a new global potential energy surface fit to a large number of high-level ab initio data. Our study shows that the major formation reaction for H2Cl+ produces this ion via a hydrogen abstraction rather than a scrambling mechanism. Such a mechanism leads to a 3:1 OPR, which is not changed by destruction and possible thermalization reactions for H2Cl+ and is thus likely to be the cause of observed 3:1 OPR ratios, contrary to the normal assumption of scrambling.},
doi = {10.1051/0004-6361/201731566},
journal = {Astronomy and Astrophysics},
number = ,
volume = 608,
place = {United States},
year = {2017},
month = {12}
}

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Works referenced in this record:

Ab Initio Calculation of Vibrational Absorption and Circular Dichroism Spectra Using Density Functional Force Fields
journal, November 1994

  • Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.
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