A new weapon for the interstellar complex organic molecule hunt: the minimum energy principle

Abstract

Context. The hunt for the interstellar complex organic molecules (COMs) supposed to be the building blocks of the molecules at the origin of life is a challenging but very expensive task. It starts with laboratory experiments, associated with theoretical calculations, that give the line frequencies and strengths of the relevant molecules to be identified and finishes with observations at the telescopes. Aims. The present study aims to suggest possible guidelines to optimize this hunt. Levering on the minimum energy principle (MEP) presented in a previous study, we discuss the link between thermodynamic stability and detectability of a number of structures in the important families of amides, sugars and aminonitriles. Methods. The question of the relative stability of these different species is addressed by means of quantum density functional theory simulations. The hybrid B3LYP formalism was used throughout. All 72 molecules part of this survey were treated on an equal footing. Each structure, fully optimized, was verified to be a stationary point by vibrational analysis. Results. A comprehensive screening of 72 isomers of CH 3 NO, C 2 H 5 NO, C 3 H 7 NO, C 2 H 4 O 2 , C 3 H 6 O 3 and C 2 H 4 N 2 chemical formula has been carried out. We found that formamide, acetamide and propanamide (the first two identified in the Inter-Stellar Medium) are the most stable compounds in their families demonstrating at the same time that the peptide bond >N-C=O at the origin of life is the most stable bond that can be formed. Dihydroxyacetone, whose detection awaits for confirmation, is far from being the most stable isomer of its family while aminoacetonitrile, that has been recently identified, is effectively the most stable species. Conclusions. The MEP appears to be a useful tool for optimizing the hunt for new species by identifying the potentially more abundant isomers of a given chemical formula.

Rotational spectroscopy, tentative interstellar detection, and chemical modeling of N-methylformamide

“…A further test would be to measure the abundance of the next C 2 H 5 NO isomer, acetimidic acid, CH 3 C(OH)NH which has a slightly higher zero-point energy than N-methylformamide (Lattelais et al 2010). This would require laboratory measurements to characterize the rotational spectrum of this molecule and produce spectroscopic predictions suitable for an astronomical search.…”

“…It is of interest as a candidate for interstellar detection because its structural isomer acetamide (CH 3 CONH 2 ) has already been detected in the ISM (Hollis et al 2006;Halfen et al 2011). CH 3 NHCHO is the second most stable C 2 H 5 NO isomer after acetamide (Lattelais et al 2010).…”

About the detectability of glycine in the interstellar medium

“…The cyclic isomers and those containing an NO bond were not considered for energetic reasons (Chiaramello et al 2005;Lattelais et al 2010).…”

Rotational spectrum of formamide up to 1 THz and first ISM detection of itsν12vibrational state

“…It is an important molecule for interstellar pre-biotic chemistry because it contains a peptide bond -C(=O)NH-that holds together the chains of amino acids. Recently it has been shown that of all possible simplest interstellar molecules that contain a peptide bond, formamide is the most stable energetically (Lattelais et al 2010). Formamide is a light molecule whose maximum absorption (emission) lies at about 650 GHz below 300 K and an intense spectrum that extends far beyond 1 THz.…”