{
  "id": "1607.00375",
  "version": "v1",
  "published": "2016-07-01T19:58:09.000Z",
  "updated": "2016-07-01T19:58:09.000Z",
  "title": "The chemistry of interstellar argonium and other probes of the molecular fraction in diffuse clouds",
  "authors": [
    "David A. Neufeld",
    "Mark G. Wolfire"
  ],
  "comment": "Accepted for publication in ApJ. 26 pages, 8 figures",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "We present a general parameter study, in which the abundance of interstellar argonium (ArH$^+$) is predicted using a model for the physics and chemistry of diffuse interstellar gas clouds. Results have been obtained as a function of UV radiation field, cosmic-ray ionization rate, and cloud extinction. No single set of cloud parameters provides an acceptable fit to the typical ArH$^+$, OH$^+$ and $\\rm H_2O^+$ abundances observed in diffuse clouds within the Galactic disk. Instead, the observed abundances suggest that ArH$^+$ resides primarily in a separate population of small clouds of total visual extinction of at most 0.02 mag per cloud, within which the column-averaged molecular fraction is in the range $10^{-5} - 10^{-2}$, while OH$^+$ and $\\rm H_2O^+$ reside primarily in somewhat larger clouds with a column-averaged molecular fraction $\\sim 0.2$. This analysis confirms our previous suggestion that the argonium molecular ion is a unique tracer of almost purely atomic gas.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2016-07-01T19:58:09.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "diffuse clouds",
      "interstellar argonium",
      "column-averaged molecular fraction",
      "diffuse interstellar gas clouds",
      "general parameter study"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 26,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}