The trans/cis ratio of formic, HCOOH, and thioformic, HC(O)SH, acids in the Interstellar Medium

Abstract

We studied theoretically the cis-trans isomerization reactions of two astrophysically relevant acids, formic acid (HCOOH) and thioformic acid (HC(O)SH), where the latter has recently been discovered in space. We also searched for these molecules towards the hot core G31.41+0.31 to compare their abundances with the expected theoretical isomerization results. Our results demonstrate that these isomerizations are viable in the conditions of the ISM due to ground-state tunneling effects, which allow the system to reach the thermodynamic equilibrium at moderately low temperatures. At very low temperatures (Tkin 10 K), the reaction rate constants for the cis to trans isomerizations are very small, which implies that the cis isomers should not be formed under cold ISM conditions. This is in disagreement with observations of the cis/trans isomers of HCOOH in cold cores where the cis isomer is found to be 5-6% the trans isomer. At high temperatures (150-300 K), our theoretical data not only match the observed behaviour of the trans/cis abundance ratios for HCOOH (the cis form is undetected), but they support our tentative detection of the trans and, for the first time in the insterstellar medium, of the cis isomer of HC(O)SH towards the hot molecular core G31.41+0.31 (with a measured trans/cis abundance ratio of 3.7). While the trans/cis ratio for HC(O)SH in the ISM depends on the relative stability of the isomers, the trans/cis ratio for HCOOH cannot be explained by isomerization, and it is determined by other competitive chemical processes

14 pages, 7 figures, 5 tables

References in corpus (25)

• The origin of complex organic molecules in prestellar cores
• The ALMA-PILS survey: Inventory of complex organic molecules towards IRAS 16293-2422 A
• The Perseus ALMA Chemistry Survey (PEACHES). I. The Complex Organic Molecules in Perseus Embedded Protostars
• The formation of ethylene glycol and other complex organic molecules in star-forming regions
• Thiols in the ISM: first detection of HC(O)SH and confirmation of C${}_2$H${}_5$SH
• Complex organic molecules in low-mass protostars on solar system scales -- I. Oxygen-bearing species
• First Abundance Measurement of Organic Molecules in the Atmosphere of HH 212 Protostellar Disk
• Propargylimine in the laboratory and in space: millimetre-wave spectroscopy and first detection in the ISM
• Chemical complexity induced by efficient ice evaporation in the Barnard 5 molecular cloud
• Orbital and mass constraints of the young binary system IRAS 16293-2422 A
• Trans-cis molecular photoswitching in interstellar Space
• The GUAPOS project II. A comprehensive study of peptide-like bond molecules
• Chemical complexity in high-mass star formation: An observational and modeling case study of the AFGL 2591 VLA 3 hot core
• The GUAPOS project: G31.41+0.31 Unbiased ALMA sPectral Observational Survey -- I. Isomers of C${}_2$H${}_4$O${}_2$
• Isomers in Interstellar Environments (I): The Case of Z- and E-Cyanomethanimine
• On the chemical ladder of esters. Detection and formation of ethyl formate in the W51 e2 hot molecular core
• Anomalous peculiar motions of high-mass young stars in the Scutum spiral arm
• The origin of the E/Z isomer ratio of imines in the interstellar medium
• The Role of State-of-the-Art Quantum-Chemical Calculations in Astrochemistry: Formation Route and Spectroscopy of Ethanimine as a Paradigmatic Case
• Methanimine as a key precursor of imines in the interstellar medium: the case of propargylimine
• Mapping Observations of complex organic molecules around Sagittarius B2 with ARO 12m telescope
• Diastereoselective Formation of trans-HC(O)SH Through Hydrogenation of OCS on Interstellar Dust Grains
• Identification of Methyl Isocyanate and Other Complex Organic Molecules in a Hot Molecular Core, G31.41+0.31
• Fragmentation in the massive G31.41+0.31 protocluster
• Anharmonic Vibrational Spectrum and Experimental Matrix Isolation Study of Thioformic Acid Conformers -- Potential Candidates for Molecular Cloud and Solar System Observations?

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• Reexploring Molecular Complexity with ALMA: Insights into chemical differentiation from the molecular composition of hot cores in Sgr B2(N2)
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• First Identification and Chemical Modeling of New Thiol ($-$SH) Bearing Molecule in the Interstellar Medium: Dithioformic Acid
• A sequential acid-base (SAB) mechanism in the interstellar medium: The emergence of cis formic acid in dark molecular clouds
• Deep Search for Glycine Conformers in Barnard 5
• Detection of monothioformic acid towards the solar-type protostar IRAS 16293-2422
• The GUAPOS project. VI: the chemical inventory of shocked gas
• Piecing together formic acid isomerism in dark clouds. Detection of cis-formic acid in TMC-1 and astrochemical modeling
• Organic Acid Chemistry in ISM: Detection of Formic Acid and its Prebiotic Chemistry in Hot Core G358.93$-$0.03 MM1
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