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