Synthesis of Formamide and Related Organic Species in the Interstellar Medium via Chemical Dynamics Simulations

Abstract

We show, by means of direct dynamics simulations, how it is possible to define possible reactants and mechanisms leading to the formation of formamide in the interstellar medium. In particular, different ion-molecule reactions in the gas phase were considered: NH 3 OH + , NH 2 OH + 2 , H 2 COH + , and NH 4 + for the ions and NH 2 OH, H 2 CO, and NH 3 for the partner neutrals. These calculations were combined with high level ab initio calculations to investigate possible further evolution of the products observed. In particular, for formamide, we propose that the NH 2 OH + 2 + H 2 CO reaction can produce an isomer, NH 2 OCH + 2 , that, after dissociative recombination, can produce neutral formamide, which was observed in space. The direct dynamics do not pre-impose any reaction pathways and in other reactions, we did not observe the formation of formamide or any possible precursor. On the other hand, we obtained other interesting reactions, like the formation of NH 2 CH + 2 . Finally, some radiative association processes are proposed. All of the results obtained are discussed in light of the species observed in radioastronomy.

Gas Phase Synthesis of Protonated Glycine by Chemical Dynamics Simulations

“…In recent work 19 we studied ion-molecule collisions for formation of protonated formamide in the gas phase at different levels of theory. The PM6-D method was chosen for the ion/molecule collision dynamics to study GlyH + synthesis for three reasons: (i) for NH 2 OH 2 + + H 2 CO it gives a fraction of the water loss pathway similar to the MP2 results and this reaction is similar to the glycine formation reaction we are interested in; (ii) it includes dispersion, which may be important for describing approach of the reactants, and thus the results may be better than PM6; and (iii) PM6-D is included in the MOPAC semi-empirical software, which is interfaced with VENUS in an optimized way such that the calculations are much faster than when using MSINDO.…”

“…Recently, we have shown that semi-empirical methods can be an alternative way to qualitatively understand reaction dynamics, mainly in the field of unimolecular dissociation, 21,22,23,24,25,26 and also in the study of ion-molecule collision, where we found that MSINDO semi-empirical Hamiltonian gives results qualitatively in agreement with MP2. 19 Here we first tested a larger variety of semi-empirical Hamiltonians on the reaction responsible to formamide formation for which we have benchmark MP2 results and thus used the one performing better to study the ion-molecule collisions of reactions 1 and 2. Present results show that both tautomers are able to react and form ions with the mass of protonated glycine but with different structures.…”

The formation of urea in space

“…Following this hypothesis, quantum chemistry calculations reported that while some possible mechanisms for the formation of formamide (Redondo et al 2014b) and glycine (Barrientos et al 2012) should be discarded due to high reaction barriers, others are possible, like the formation of acetamide through H 2 NCHO + CH + 5 reaction (Redondo et al 2014a) or formamide through a radical mechanism (Barone et al 2015). Ion-molecule collisions were suggested as a possible mechanism in both experimental (Geppert & Larsson 2013;Larsson et al 2012;Blagojevic et al 2003;Petrie & Bohme 2007;Snow et al 2007) and theoretical studies (Spezia et al 2016). In this case even reactions with (small) activation barriers are possible thanks to the transformation in the collision of some of the translational energy into internal energy.…”

Interstellar Formamide (NH2CHO), a Key Prebiotic Precursor

“…In particular, they adopted the γ value from the former and the α and β values from the latter, Several ion-molecule reactions have also been considered from a theoretical point of view. [134][135][136] In particular, reactions involving ionic or protonated forms of nitrogen com-…”