Theoretical study of amines containing molecules in the gas and water solvent

Abstract

This study reports the infrared and electronic absorption spectra of amine-containing molecules. We investigate how these spectra differ for molecules in their neutral and ionic forms in gas and astrophysical H2O ice. Additionally, we analyze the pure rotational spectra of these molecules in the gas state. These are prebiotic molecules such as propargylamine (C3H5N), four isomers of C3H7N (1-aminopropene, 2-propenamine, allylamine, and cyclopropylamine), and two isomers of C3H9N (n-propyl amine and 2-aminpropane) considered for the study. We analyzed various properties of molecules in different states: gas phase, water solvent, and ionic states. We used the coupled-cluster method (CCSD) with a 6–311++G** basis set for our studies. The rotational constants obtained at this level of theory are well matching with the available experimental determinations. These constants are further used to calculate the rotational spectra and their transitions. The calculated vibrational frequencies of these molecules matched well with experimental results at this level of theory. To study the influence of solvent, we employed the IEFPCM model at the same level of theory. We used the equation of motion coupled cluster theory (EOM-CCSD) at the CCSD/6–311++G** level of theory to examine the electronic absorption spectra. We reported the HOMO-LUMO gap, electronic transitions, and oscillator strength of these transitions. We identified the best lines from microwave and infrared regions to observe these molecules in interstellar environments. All calculations were performed using the Gaussian 16 and PGOPHER program packages.