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Title: Collisional excitation of CH2 rotational/fine-structure levels by helium

Abstract

Accurate determination of the abundance of CH2 in interstellar media relies on both radiative and collisional rate coefficients. Here, we investigate here the rotational/fine-structure excitation of CH2 induced by collisions with He. We employ a recoupling technique to generate fine-structure-resolved cross-sections and rate coefficients from close coupling spin-free scattering calculations. The calculations are based on a recent, high-accuracy CH2–He potential energy surface computed at the coupled clusters level of theory. The collisional cross-section calculations are performed for all fine-structure transitions among the first 22 and 24 energy levels of ortho- and para-CH2, respectively, and for temperatures up to 300 K. As a first application, we simulate the excitation of CH2 in typical molecular clouds. The excitation temperatures of the CH2 lines are found to be small at typical densities of molecular clouds, showing that the non-local thermodynamic equilibrium approach has to be used to analyse interstellar spectra. We also found that the fine-structure lines connected with the 404 – 313 and 505 – 414 rotational transitions show possible maser emissions so that they can be easily seen in emission. In conclusion, these calculations show that CH2 may have to be detected mainly through absorption spectra.

Authors:
 [1];  [2]
+ Show Author Affiliations
  1. Johns Hopkins Univ., Baltimore, MD (United States)
  2. CNRS-Université du Havre (France); Univ. of Maryland, College Park, MD (United States)
Publication Date:
Research Org.:
Univ. of Maryland, College Park, MD (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
OSTI Identifier:
1512963
Grant/Contract Number:  
SC0002323
Resource Type:
Accepted Manuscript
Journal Name:
Monthly Notices of the Royal Astronomical Society
Additional Journal Information:
Journal Volume: 473; Journal Issue: 4; Journal ID: ISSN 0035-8711
Publisher:
Royal Astronomical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 79 ASTRONOMY AND ASTROPHYSICS; molecular data; molecular processes; ISM: abundances

Citation Formats

Dagdigian, P. J., and Lique, F. Collisional excitation of CH2 rotational/fine-structure levels by helium. United States: N. p., 2017. Web. doi:10.1093/mnras/stx2697.
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Dagdigian, P. J., & Lique, F. Collisional excitation of CH2 rotational/fine-structure levels by helium. United States. https://doi.org/10.1093/mnras/stx2697
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Dagdigian, P. J., and Lique, F. Sat . "Collisional excitation of CH2 rotational/fine-structure levels by helium". United States. https://doi.org/10.1093/mnras/stx2697. https://www.osti.gov/servlets/purl/1512963.
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@article{osti_1512963,
title = {Collisional excitation of CH2 rotational/fine-structure levels by helium},
author = {Dagdigian, P. J. and Lique, F.},
abstractNote = {Accurate determination of the abundance of CH2 in interstellar media relies on both radiative and collisional rate coefficients. Here, we investigate here the rotational/fine-structure excitation of CH2 induced by collisions with He. We employ a recoupling technique to generate fine-structure-resolved cross-sections and rate coefficients from close coupling spin-free scattering calculations. The calculations are based on a recent, high-accuracy CH2–He potential energy surface computed at the coupled clusters level of theory. The collisional cross-section calculations are performed for all fine-structure transitions among the first 22 and 24 energy levels of ortho- and para-CH2, respectively, and for temperatures up to 300 K. As a first application, we simulate the excitation of CH2 in typical molecular clouds. The excitation temperatures of the CH2 lines are found to be small at typical densities of molecular clouds, showing that the non-local thermodynamic equilibrium approach has to be used to analyse interstellar spectra. We also found that the fine-structure lines connected with the 404 – 313 and 505 – 414 rotational transitions show possible maser emissions so that they can be easily seen in emission. In conclusion, these calculations show that CH2 may have to be detected mainly through absorption spectra.},
doi = {10.1093/mnras/stx2697},
journal = {Monthly Notices of the Royal Astronomical Society},
number = 4,
volume = 473,
place = {United States},
year = {Sat Oct 14 00:00:00 EDT 2017},
month = {Sat Oct 14 00:00:00 EDT 2017}
}
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Journal Article:
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Publisher's Version of Record
https://doi.org/10.1093/mnras/stx2697
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Cited by: 5 works
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Figures / Tables:

Figure 1 Figure 1: Energies of the low-lying rotational levels of CH2(X̃3B1) and the approximate frequencies (in GHz) of the allowed transitions between these levels. The ortho 220 level is connected to the 211 and 111 levels by transitions at 4925 and 5934 GHz (labelled A and B), respectively, and the paramore » 221 level is connected to the 212 and 110 levels by transitions at 5022 and 5895 GHz (labelled C and D), respectively, The fine-structure splittings are too small to be visible in the figure.« less
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Works referenced in this record:

Infrared and far-infrared transition frequencies for the CH2 radical
journal, January 1984

  • Sears, T. J.; McKellar, A. R. W.; Bunker, P. R.
  • The Astrophysical Journal, Vol. 276
  • DOI: 10.1086/161624

High-resolution terahertz spectrum of CH 2 — Low J rotational transitions near 2 THz
journal, June 2004

  • Brünken, S.; Michael, E. A.; Lewen, F.
  • Canadian Journal of Chemistry, Vol. 82, Issue 6
  • DOI: 10.1139/v04-034

Confirmation of interstellar methylene
journal, January 1995

  • Hollis, J. M.; Jewell, P. R.; Lovas, F. J.
  • The Astrophysical Journal, Vol. 438
  • DOI: 10.1086/175070

Can we estimate H$\mathsf{_{2}}$( j = 0) rate coefficients from He rate coefficients? Application to the SiS molecule
journal, December 2007

Interstellar Hydrides
journal, September 2016

A computer program for fast non-LTE analysis of interstellar line spectra: With diagnostic plots to interpret observed line intensity ratios
journal, April 2007

  • van der Tak, F. F. S.; Black, J. H.; Schöier, F. L.
  • Astronomy & Astrophysics, Vol. 468, Issue 2
  • DOI: 10.1051/0004-6361:20066820

BASECOL2012: A collisional database repository and web service within the Virtual Atomic and Molecular Data Centre (VAMDC)
journal, April 2013

Hyperfine excitation of CN by para- and ortho-H2
journal, October 2014

  • Kalugina, Yulia; Lique, François
  • Monthly Notices of the Royal Astronomical Society: Letters, Vol. 446, Issue 1
  • DOI: 10.1093/mnrasl/slu159

Hyperfine excitation of CN by He: Hyperfine excitation of CN by He
journal, February 2011

Laboratory Spectrum of the 1 11 –2 02 Rotational Transition of CH 2
journal, October 2003

  • Michael, Ernest A.; Lewen, Frank; Winnewisser, Gisbert
  • The Astrophysical Journal, Vol. 596, Issue 2
  • DOI: 10.1086/378090

Observations of HCN hyperfine line anomalies towards low- and high-mass star-forming cores: Observations of HCN hyperfine line anomalies
journal, December 2011

Molecular Excitation in the Interstellar Medium: Recent Advances in Collisional, Radiative, and Chemical Processes
journal, October 2013

  • Roueff, Evelyne; Lique, François
  • Chemical Reviews, Vol. 113, Issue 12
  • DOI: 10.1021/cr400145a

The vibration-rotation problem in triatomic molecules allowing for a large-amplitude bending vibration
journal, April 1970

Fine and hyperfine excitation of C2H by collisions with He at low temperature: Fine and hyperfine excitation of C2H by He
journal, March 2012

Theoretical investigation of rotationally inelastic collisions of CH 2 (X̃) with helium
journal, June 2012

  • Dagdigian, Paul J.; Alexander, Millard H.
  • The Journal of Chemical Physics, Vol. 136, Issue 22
  • DOI: 10.1063/1.4729050

Theoretical investigation of rotationally inelastic collisions of CH 2 ( ã ) with helium
journal, April 2011

  • Ma, Lifang; Alexander, Millard H.; Dagdigian, Paul J.
  • The Journal of Chemical Physics, Vol. 134, Issue 15
  • DOI: 10.1063/1.3575200

Hyperfine excitation of OH + by H
journal, July 2016

  • Lique, François; Bulut, Niyazi; Roncero, Octavio
  • Monthly Notices of the Royal Astronomical Society, Vol. 461, Issue 4
  • DOI: 10.1093/mnras/stw1638

Far-infrared detection of methylene
journal, February 2005

A Search for Interstellar CH 2 toward HD 154368 and ζ Ophiuchi
journal, October 2001

  • Lyu, Cheng‐Hsuan; Smith, Andrew M.; Bruhweiler, Frederick C.
  • The Astrophysical Journal, Vol. 560, Issue 2
  • DOI: 10.1086/322426

The hyperfine excitation of OH radicals by He
journal, April 2016

  • Marinakis, Sarantos; Kalugina, Yulia; Lique, François
  • The European Physical Journal D, Vol. 70, Issue 4
  • DOI: 10.1140/epjd/e2016-70068-x

State-resolved thermalization of singlet and mixed singlet-triplet states of CH2
journal, August 2006

  • Komissarov, Anatoly V.; Lin, Ao; Sears, Trevor J.
  • The Journal of Chemical Physics, Vol. 125, Issue 8
  • DOI: 10.1063/1.2345364

Stratified NH and ND emission in the prestellar core 16293E in L1689N
journal, February 2016

Isotope effects in the fragmentation of water: The photodissociation of HOD in the first absorption band
journal, June 1988

  • Engel, V.; Schinke, R.
  • The Journal of Chemical Physics, Vol. 88, Issue 11
  • DOI: 10.1063/1.454381

An atomic and molecular database for analysis of submillimetre line observations
journal, February 2005

  • Schöier, F. L.; van der Tak, F. F. S.; van Dishoeck, E. F.
  • Astronomy & Astrophysics, Vol. 432, Issue 1
  • DOI: 10.1051/0004-6361:20041729

The impact of collisional rate coefficients on molecular hyperfine selective excitation: Molecular hyperfine selective excitation
journal, July 2012

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    The Leiden Atomic and Molecular Database (LAMDA): Current Status, Recent Updates, and Future Plans
    preprint, January 2020

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