Providing theoretical data for detection of four formamidic acid isomers in astrophysical media

Author(s)

Vichietti, R. M. ^[1] ; da Silva, A. B. F. ^[1] ; Haiduke, R. L. A. ^[1]

Affiliation

^[1] Univ Sao Paulo, Inst Quim Sao Carlos, Dept Quim & Fis Mol, CP 780, BR-13560970 Sao Carlos, SP - Brazil

• Document type: Journal article
• Source: MOLECULAR ASTROPHYSICS; v. 10, p. 1-10, MAR 2018.
• Web of Science Citations: 1

Abstract

We present a theoretical study, so that molecular data (geometrical parameters, vibrational frequencies, infrared intensities, electronic energies, enthalpies, and Gibbs energies) of four formamidic acid (FA) isomers (labeled here as FA1, FA2, FA3, and FA4) and formamide (HCONH2) are obtained from CCSD/ccpVTZ, CCSD/aug-cc-pVTZ, CCSD/cc-pVQZ, and CCSD(T)/cc-pVTZ calculations. Furthermore, on the basis of insufficient or even lacking theoretical and experimental results in the literature, we employed the aforementioned theory levels to determine benchmark values of dipole moments and rotational constants for these four FA isomers in order to contribute for their detection in astrophysical environments. Besides, we provide for the first time data about forward and reverse rate constants (200-4000 K) and Arrhenius' parameters for each interconversion reaction between pairs of FA isomers as well as for the tautomeric process involving FA4 and formamide, which were calculated from a Complete Basis Set (CBS) extrapolation equation obtained at CCSD/cc-pVTZ optimized geometries. Our kinetic analysis indicated a faster interconversion between the FA structures in comparison with the FA4 <-> HCONH2 process, suggesting that these isomers could co-exist in astrophysical media. Finally, we estimated that these isomers may be detected with relative abundances, {[}FA(x)]/{[}HCONH2] (x = 1, 2, 3, and 4), between similar to 0.01 and similar to 0.1% in astrophysical sources at chemical equilibrium conditions and temperatures around 10 0 0 K. However, these ratios can become as high as similar to 1, similar to 3, and similar to 5%, respectively, in hotter regions with temperatures around 20 0 0, 30 0 0, and 40 0 0 K (expected, for example, in massive star-forming regions). (C) 2018 Elsevier B.V. All rightsreserved. (AU)

• FAPESP's process: 14/23714-1 - Electronic structure relativistic calculations for evaluation of new prolapse-free basis sets
• Grantee: Roberto Luiz Andrade Haiduke
• Support type: Regular Research Grants
• FAPESP's process: 10/18743-1 - Employment of multipoles from the quantum theory of atoms in molecules and kinetic studies in systems found in the interstellar medium
• Grantee: Roberto Luiz Andrade Haiduke
• Support type: Regular Research Grants