Observations of H3+ in the diffuse interstellar medium

B. J. McCall; K. H. Hinkle; T. R. Geballe; G. H. Moriarty-Schieven; N. J. Evans; K. Kawaguchi; S. Takano; V. V. Smith; T. Oka

doi:10.1086/338380

Observations of H₃⁺ in the diffuse interstellar medium

B. J. McCall, K. H. Hinkle, T. R. Geballe, G. H. Moriarty-Schieven, N. J. Evans, K. Kawaguchi, S. Takano, V. V. Smith, T. Oka

Chemistry

Research output: Contribution to journal › Article › peer-review

Abstract

Surprisingly large column densities of H₃⁺ have been detected using infrared absorption spectroscopy in seven diffuse cloud sight lines (Cygnus OB2 12, Cygnus OB2 5, HD 183143, HD 20041, WR 104, WR 118, and WR 121), demonstrating that H₃⁺ is ubiquitous in the diffuse interstellar medium. Using the standard model of diffuse cloud chemistry, our H₃⁺ column densities imply unreasonably long path lengths (∼1 kpc) and low densities (∼3 cm^-3). Complimentary millimeter-wave, infrared, and visible observations of related species suggest that the chemical model is incorrect and that the number density of H ₃⁺ must be increased by 1-2 orders of magnitude. Possible solutions include a reduced electron fraction, an enhanced rate of H ₂ ionization, and/or a smaller value of the H₃ ⁺ dissociative recombination rate constant than implied by laboratory experiments.

Original language	English (US)
Pages (from-to)	391-406
Number of pages	16
Journal	Astrophysical Journal
Volume	567
Issue number	1 I
DOIs	https://doi.org/10.1086/338380
State	Published - Mar 1 2002

Keywords

Cosmic rays
ISM: clouds
ISM: molecules
Infrared: ISM: lines and bands
Molecular processes

ASJC Scopus subject areas

Astronomy and Astrophysics
Space and Planetary Science

Online availability

10.1086/338380

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title = "Observations of H3+ in the diffuse interstellar medium",

abstract = "Surprisingly large column densities of H3+ have been detected using infrared absorption spectroscopy in seven diffuse cloud sight lines (Cygnus OB2 12, Cygnus OB2 5, HD 183143, HD 20041, WR 104, WR 118, and WR 121), demonstrating that H3+ is ubiquitous in the diffuse interstellar medium. Using the standard model of diffuse cloud chemistry, our H3+ column densities imply unreasonably long path lengths (∼1 kpc) and low densities (∼3 cm-3). Complimentary millimeter-wave, infrared, and visible observations of related species suggest that the chemical model is incorrect and that the number density of H 3+ must be increased by 1-2 orders of magnitude. Possible solutions include a reduced electron fraction, an enhanced rate of H 2 ionization, and/or a smaller value of the H3 + dissociative recombination rate constant than implied by laboratory experiments.",

keywords = "Cosmic rays, ISM: clouds, ISM: molecules, Infrared: ISM: lines and bands, Molecular processes",

author = "McCall, {B. J.} and Hinkle, {K. H.} and Geballe, {T. R.} and Moriarty-Schieven, {G. H.} and Evans, {N. J.} and K. Kawaguchi and S. Takano and Smith, {V. V.} and T. Oka",

year = "2002",

month = mar,

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doi = "10.1086/338380",

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volume = "567",

pages = "391--406",

journal = "Astrophysical Journal",

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T1 - Observations of H3+ in the diffuse interstellar medium

AU - McCall, B. J.

AU - Hinkle, K. H.

AU - Geballe, T. R.

AU - Moriarty-Schieven, G. H.

AU - Evans, N. J.

AU - Kawaguchi, K.

AU - Takano, S.

AU - Smith, V. V.

AU - Oka, T.

PY - 2002/3/1

Y1 - 2002/3/1

N2 - Surprisingly large column densities of H3+ have been detected using infrared absorption spectroscopy in seven diffuse cloud sight lines (Cygnus OB2 12, Cygnus OB2 5, HD 183143, HD 20041, WR 104, WR 118, and WR 121), demonstrating that H3+ is ubiquitous in the diffuse interstellar medium. Using the standard model of diffuse cloud chemistry, our H3+ column densities imply unreasonably long path lengths (∼1 kpc) and low densities (∼3 cm-3). Complimentary millimeter-wave, infrared, and visible observations of related species suggest that the chemical model is incorrect and that the number density of H 3+ must be increased by 1-2 orders of magnitude. Possible solutions include a reduced electron fraction, an enhanced rate of H 2 ionization, and/or a smaller value of the H3 + dissociative recombination rate constant than implied by laboratory experiments.

AB - Surprisingly large column densities of H3+ have been detected using infrared absorption spectroscopy in seven diffuse cloud sight lines (Cygnus OB2 12, Cygnus OB2 5, HD 183143, HD 20041, WR 104, WR 118, and WR 121), demonstrating that H3+ is ubiquitous in the diffuse interstellar medium. Using the standard model of diffuse cloud chemistry, our H3+ column densities imply unreasonably long path lengths (∼1 kpc) and low densities (∼3 cm-3). Complimentary millimeter-wave, infrared, and visible observations of related species suggest that the chemical model is incorrect and that the number density of H 3+ must be increased by 1-2 orders of magnitude. Possible solutions include a reduced electron fraction, an enhanced rate of H 2 ionization, and/or a smaller value of the H3 + dissociative recombination rate constant than implied by laboratory experiments.

KW - Cosmic rays

KW - ISM: clouds

KW - ISM: molecules

KW - Infrared: ISM: lines and bands

KW - Molecular processes

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