Accurate Enthalpies of Formation of Astromolecules: Energy, Stability and Abundance

TL;DR

This study uses high-level quantum chemical calculations to determine accurate enthalpies of formation for 130 astromolecules, revealing a strong correlation between molecular stability and abundance in space, aiding future astronomical observations.

Contribution

It provides the first comprehensive analysis linking energy, stability, and abundance of astromolecules, with implications for identifying molecules in space.

Findings

Lower enthalpy isomers are more abundant in the interstellar medium.

Most stable isomers tend to be more abundant, confirming the stability-abundance relationship.

Some experimental data may be unreliable, suggesting need for new measurements.

Abstract

Accurate enthalpies of formation are reported for known and potential astromolecules using high level ab initio quantum chemical calculations. A total of 130 molecules comprising of 31 isomeric groups and 24 cyanide/isocyanide pairs with atoms ranging from 3 to 12 have been considered. The results show an interesting, surprisingly not well explored, relationship between energy, stability and abundance (ESA) existing among these molecules. Among the isomeric species, isomers with lower enthalpies of formation are more easily observed in the interstellar medium compared to their counterparts with higher enthalpies of formation. Available data in literature confirm the high abundance of the most stable isomer over other isomers in the different groups considered. Potential for interstellar hydrogen bonding accounts for the few exceptions observed. Thus, in general, it suffices to say that the interstellar abundances of related species are directly proportional to their stabilities. The immediate consequences of this relationship in addressing some of the whys and wherefores among astromolecules and in predicting some possible candidates for future astronomical observations are discussed. Our comprehensive results on 130 molecules indicate that the available experimental enthalpy of formation for some molecules, such as NaCN, may be less reliable and new measurements may be needed.