Rotational and vibrational analysis of astrophysically relevant isomeric species of proteinogenic glutamic acid: A quantum-mechanical computational study

Abstract

There has been growing curiosity in finding complex organic molecules such as proteinogenic amino acids in outer space. The life-supporting amino acids have been detected in the meteoritic samples with enantiomeric excess; however, their detection in the interstellar medium (ISM) has remained elusive so far. The spectral information received from ISM is often too complex to resolve for confirming the presence of a large-sized molecular species such as glutamic acid. The rotational and vibrational spectroscopy is the key to detection of such molecules in ISM. This work provides pure rotational and vibrational line data through quantum mechanical computations for glutamic acid and isomeric molecular species proposed along its gas-phase stereoinversion pathways under conditions akin to the ISM. The molecular species investigated in this work form a network of diverse molecules, which include zwitterionic ammonium ylide, di-carboxylic acid, gem-diol, vicinal-diol and imine. Notably, anharmonic calculations using vibrational second order perturbation theory have been performed to accurately predict the rotational and vibrational transitions, particularly in millimetre (mm), sub-mm, mid- and far-infrared regions, which can assist in the detection of glutamic acid in different regions of ISM.