Ab initio studies on cyanoacetylenes of astrochemical interest: [Y(CC)CN, Y C2H5, C3H7, C4H9, F, Cl, Br and CN]

• Structural and spectroscopic data of cyanoacetylenes were computed using theoretical methods.
• Comparisons of these parameters with experiments indicate the good performance of DFT method.
• The large electric dipole moment of the cyanoacetylenes should help towards their detections.
• The theoretical findings of these cyanoacetylenes should be helpful to experimentalists.
• Plausible formation mechanisms of the cyanoacetylenes are also proposed.

Theoretical studies were performed on seven potential interstellar and circumstellar substituted cyanoacetylenes, Y(CC)CN [Y = C2H5, C3H7, C4H9, F, Cl, Br and CN]. Geometry optimizations were carried out using the DFT/B3LYP, the CCSD and CCSD(T) levels of theory. The cc-pVTZ basis set was used for all atoms. Frequency computations were also carried out at the same level of theory as for the optimization to check the nature of the stationary points. The molecular and spectroscopic parameters of the cyanoacetylenes were computed. An analysis of these parameters is in line with the satisfactory performance of the B3LYP/cc-pVTZ level compared to the golden standard, the CCSD(T) level. The theoretical data reported in this work should facilitate future identifications of these cyanoacetylenes in extraterrestrial locations. Plausible mechanisms for the formation of these molecules have been proposed.

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