The observed ratios of COM isomers in the ISM provide valuable information about the chemistry and physics of gases and, ultimately, the history of molecular clouds.
The content of the c-HCOOH acid in the cold core is only 6% of the content of the c-HCOOH isomer, and its origin remains unknown. Here we explain the presence of c-HCOOH in dark molecular clouds by the destruction and reduction of c-HCOOH and t-HCOOH during cycles involving HCOOH and very abundant molecules such as HCO+ and NH3.
We used an extended ab initio approach to calculate the potential energy distribution for the c-HCOOH and t-HCOOH breakdown/cycling pathways. Global rate constants and branching factors were calculated based on the transition state theory and the form of the master equation under typical ISM conditions.
HCOOH is destroyed upon interaction with HCO+ in the gas phase to form three isomers of the HC(OH)2+ cation. The most common cations can react with other common molecules in the ISM, such as NH3, in a second step to convert c-HCOOH and t-HCOOH. This mechanism explains the formation of c-HCOOH in dark molecular clouds. Taking this mechanism into account, the proportion of c-HCOOH relative to t-HCOOH was 25.7%.
To explain the reported 6% of observations, we propose to consider an additional mechanism for the destruction of the HCOOH cation. The sequential acid-base (SAB) mechanism proposed in this work involves a fast process of molecules very common in ISM.
Therefore, HCOOH is likely to undergo the transition we proposed under dark molecular cloud conditions. This is a new approach within the isomerism of organic molecules in the ISM, which may try to explain the relationships between the isomers of organic molecules found in the ISM.
John Garcia, Ezraquen Jimenez-Serra, Jose Carlos Colchado, Germaine Morpeceres, Antonio Martinez-Henares, Victor M. Rivera, Laura Corzi, Jesus Martin-Painde
Subjects: Galactic Astrophysics (astro-ph.GA), Chemical Physics (physical.chem-ph) Cited as: arXiv:2301.07450 [astro-ph.GA] (or this version arXiv:2301.07450v1 [astro-ph.GA] ) Commit history by: Juan Garcia de la Concepción [v1] Wednesday 18 January 2023 11:45:25 UTC (1909 KB) https://arxiv.org/abs/2301.07450 Astrobiology, astrochemistry
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