Spontaneous formation and protonation of dicyanofuran isomers under physical conditions found in interstellar space: quantum chemical insights into thermodynamics and spectroscopy

Abstract

Thermodynamic and spectroscopic data on the formation and protonation of furans and their nitrile-disubstituted derivatives are missing from the literature. These data are very important in astrophysics and astrochemistry for the detection of new species in the interstellar medium (ISM). The discovery of these species in the ISM has not been reported. The formation of dicyanofurans and their protonation under ISM conditions of pressure and temperature were investigated using computational models (G2MP2, G3B3, G3 and G4). To identify the preferential site of protonation, the proton affinity (PA) was calculated at different sites of molecules. The enthalpy change (Δ_rH), entropy change (Δ_rS), and change in Gibbs free energy (Δ_rG) of protonation were calculated at different temperatures (5 K, 10 K, 150 K and 298.15 K) at a pressure of 1 atm. The nitrogen atom of the furthest –CN functional group from the heteroatom was identified as the preferential site of protonation of dicyanofurans. On the basis of the negative values of Δ_rH, Δ_rS and Δ_rG, spontaneous reactions producing these species under ISM conditions of temperature and pressure were suggested. The quadrupole hyperfine structures and vibrational spectra (essential tools for the characterization and identification of interstellar molecular species) were predicted in the region where brightest lines fall for different temperatures. We expect the results reported herein to assist astrophysicists and astrochemists in the discovery of new chemical compounds in the ISM environment.