Proton leap: shuttling of protons onto benzonitrile

The detailed description of chemical transformations in the interstellar medium allows deciphering the origin of a number of small and medium - sized organic molecules. We present density functional theory analysis of proton transfer from the trihydrogen cation and the ethenium cation to benzonitrile, a recently discovered species in the Taurus Molecular Cloud 1. Detailed energy transformations along the reaction paths were analyzed using the interacting quantum atoms methodology, which elucidated how the proton carrier influences the lightness to deliver the proton to benzonitrile's nitrogen atom. The proton carriers' deformation energy represents the largest destabilizing effect, whereas a proton's promotion energy, the benzonitrile-proton Coulomb attraction, as well as non-classical benzonitrile-proton and carrier-proton interaction are the dominant stabilizing energy components. As two ion-molecule reactions proceed without energy barriers, rate constants were estimated using the classical capture theory and were found to be an order of magnitude larger for the reaction with the trihydrogen cation compared to that with the ethenium cation (similar to 10(-8) and 10(-9) cm(3) s(-1), respectively). These results were obtained both with quantum chemical and ab initio molecular dynamics simulations (the latter performed at 10 K and 100 K), confirming that up to 100 K both systems choose energetically undemanding routes by tracking the corresponding minimum energy paths. A concept of a turning point is introduced, which is an equivalent to the transition state in barrierless reactions.

Automated summary

The detailed description of chemical transformations in the interstellar medium allows deciphering the origin of a number of small and medium-sized organic molecules. In this study, density functional theory was used to analyze the proton transfer process from the trihydrogen cation and ethenium cation to benzonitrile. The results showed that the proton carrier's deformation energy had the largest destabilizing effect, while the proton's promotion energy, Coulomb attraction, and the interactions between benzonitrile-proton and carrier-proton were the dominant stabilizing factors. The reaction with the trihydrogen cation had a significantly higher rate constant compared to that with the ethenium cation.