Structure and spectroscopic properties of imine acetaldehyde: a possible interstellar molecule

Abstract

A previous theoretical study shows that imine acetaldehyde can be obtained from the reaction between protonated vinyl alcohol and azanone. Therefore, imine acetaldehyde could be considered as a good molecule candidate to be found in space and could evolve to more complex organic molecules of prebiotic interest. In this work, we carried out a computational study of the different conformers of imine acetaldehyde. To characterize its conformers we apply a composite approach which considers the extrapolation to the complete basis set limit and core-valence electron correlation corrections at the couplet clusters level including single and double excitations and a perturbative treatment of triple excitations. This approach provides bond distances with an accuracy of 0.001–0.002 Å and angles accurate to 0.05–0.1°. Vibrational harmonic and anharmonic frequencies and infrared intensities are also reported at the CCSD level. The most stable structure corresponds to an antiperiplanar disposition of the oxygen atom and of NH group with the hydrogen atom of the NH group addressed outside the skeleton. Interconversion processes between the four conformers characterized are studied. The lowest isomerization barrier is estimated to be around 1.2 kcal mol−1, making these processes unlikely under low-temperature conditions, such as those reigning in the interstellar medium. We reported, at ‘spectroscopic’ accuracy, stabilities, molecular structures, as well as spectroscopic parameters for the four imine acetaldehyde conformers that could help in their laboratory or astronomical detection.