{
  "id": "2406.02961",
  "version": "v1",
  "published": "2024-06-05T05:31:58.000Z",
  "updated": "2024-06-05T05:31:58.000Z",
  "title": "Carbon Isotope Fractionation of Complex Organic Molecules in Star-Forming Cores",
  "authors": [
    "Ryota Ichimura",
    "Hideko Nomura",
    "Kenji Furuya"
  ],
  "doi": "10.3847/1538-4357/ad47ba",
  "categories": [
    "astro-ph.SR",
    "astro-ph.EP",
    "astro-ph.GA"
  ],
  "abstract": "Recent high-resolution and sensitivity ALMA observations have unveiled the carbon isotope ratios ($^{12}$C/$^{13}$C) of Complex Organic Molecules (COMs) in a low-mass protostellar source. To understand the $^{12}$C/$^{13}$C ratios of COMs, we investigated the carbon isotope fractionation of COMs from prestellar cores to protostellar cores with a gas-grain chemical network model. We confirmed that the $^{12}$C/$^{13}$C ratios of small molecules are bimodal in the prestellar phase: CO and species formed from CO (e.g., CH$_{3}$OH) are slightly enriched in $^{13}$C compared to the local ISM (by $\\sim$ 10 $\\%$), while those from C and C$^{+}$ are depleted in $^{13}$C owing to isotope exchange reactions. COMs are mainly formed on the grain surface and in the hot gas ($>$ 100 K) in the protostellar phase. The $^{12}$C/$^{13}$C ratios of COMs depend on which molecules the COMs are formed from. In our base model, some COMs in the hot gas are depleted in $^{13}$C compared to the observations. Thus, We additionally incorporate reactions between gaseous atomic C and H$_{2}$O ice or CO ice on the grain surface to form H$_2$CO ice or \\ce{C2O} ice, as suggested by recent laboratory studies. The direct C-atom addition reactions open pathways to form \\ce{^13C}-enriched COMs from atomic C and CO ice. We find that these direct C-atom addition reactions mitigate $^{13}$C-depletion of COMs, and the model with the direct C-atom addition reactions better reproduces the observations than our base model. We also discuss the impact of the cosmic ray ionization rate on the $^{12}$C/$^{13}$C ratio of COMs.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2024-06-05T05:31:58.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "complex organic molecules",
      "carbon isotope fractionation",
      "direct c-atom addition reactions",
      "c-atom addition reactions mitigate",
      "addition reactions better reproduces"
    ],
    "tags": [
      "journal article"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}