The observed abundance ratios of COM isomers in the ISM provide valuable information about the chemistry and physics of gases and, ultimately, the history of the molecular cloud.
The content of the c-HCOOH acid in the cold core is only 6% of the amount of the c-HCOOH isomer, the origin of which remains unknown. Here we explain the presence of c-HCOOH in dark molecular clouds by the destruction and anti-formation of c-HCOOH and t-HCOOH during a cycling process involving HCOOH and very abundant molecules such as HCO+ and NH3.
We used an advanced ab initio method to calculate the potential energy distribution of c-HCOOH and t-HCOOH cyclic breakdown/formation pathways. The 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.
The destruction of HCOOH by reaction with HCO+ in the gas phase leads to three isomers of the HC(OH)2+ cation. The most common cations can react with other common ISM molecules such as NH3 in a second step to form back to 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 observed 6%, we propose to consider additional mechanisms 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 transformation we proposed under dark molecular cloud conditions. This is a novel approach within the isomerization of organic molecules in the ISM, potentially trying to explain the relationships between the isomers of organic molecules found in the ISM.
John Garcia, Isascun Jimenez-Serra, Jose Carlos Corchado, Germaine Molpeceres, Antonio Martinez-Henares, Victor M. Rivilla, Laura Colzi, Jesus Martin-Painted
Subject: Galactic Astrophysics (astro-ph.GA), Chemical Physics (physics.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/2301.07450Astrobiology, astrochemistry
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