{
  "id": "2110.15881",
  "version": "v1",
  "published": "2021-10-29T16:08:45.000Z",
  "updated": "2021-10-29T16:08:45.000Z",
  "title": "Methane formation in cold regions from carbon atoms and molecular hydrogen",
  "authors": [
    "Thanja Lamberts",
    "Gleb Fedoseev",
    "Marc van Hemert",
    "Danna Qasim",
    "Ko-Ju Chuang",
    "Julia C. Santos",
    "Harold Linnartz"
  ],
  "comment": "Submitted to ApJ",
  "categories": [
    "astro-ph.GA",
    "astro-ph.SR"
  ],
  "abstract": "Methane is typically thought to be formed in the solid state on the surface of cold interstellar icy grain mantles via the successive atomic hydrogenation of a carbon atom. In the current work we investigate the potential role of molecular hydrogen in the CH$_4$ reaction network. We make use of an ultra-high vacuum cryogenic setup combining an atomic carbon atom beam and both atomic and/or molecular beams of hydrogen and deuterium on a H$_2$O ice. These experiments lead to the formation of methane isotopologues detected in situ through reflection absorption infrared spectroscopy. Most notably, CH$_4$ is formed in an experiment combining C atoms with H$_2$ on amorphous solid water, albeit slower than in experiments with H atoms present. Furthermore, CH$_2$D$_2$ is detected in an experiment of C atoms with H$_2$ and D$_2$ on H$_2$O ice. CD$_4$, however, is only formed when D atoms are present in the experiment. These findings have been rationalized by means of computational chemical insights. This leads to the following conclusions: a) the reaction C + H$_2$ -> CH$_2$ can take place, although not barrierless in the presence of water, b) the reaction CH + H$_2$ -> CH$_3$ is barrierless, but has not yet been included in astrochemical models, c) the reactions CH$_2$ + H$_2$ -> CH$_3$ + H and CH$_3$ + H$_2$ -> CH$_4$ + H can take place only via a tunneling mechanism and d) molecular hydrogen possibly plays a more important role in the solid-state formation of methane than assumed so far.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2021-10-29T16:08:45.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "molecular hydrogen",
      "cold regions",
      "methane formation",
      "vacuum cryogenic setup combining",
      "cold interstellar icy grain mantles"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}