Formation of Protonated Glycine Isomers in the Interstellar Medium

Abstract

A computational study of protonated glycine isomers with [H6C2O2N]+ molecular formula has been carried out. All of them are possible products of the reaction between protonated hydroxylamine and acetic acid. All reaction processes that could form the [H6C2O2N]+ isomers considered in this work are exothermic except for those initiated by the most stable isomer of protonated hydroxylamine which give CH3CONH2+OH and CH3COHNOH2+ isomers. The analysis of the potential energy surfaces corresponding to the reaction of protonated hydroxylamine and acetic acid has been focused on the most abundant products, namely, CH3CONH2+OH, CH3COONH3+, and CH3C(OH)+ONH2, obtained from a previous chemical dynamics simulations study. From this analysis we found that even if the reactions of formation of the CH3COONH3+ and the CH3C(OH)+ONH2 isomers are exothermic processes, significant activation barriers were found in the paths leading to these products. The only exothermic process (ΔE = −23.9 kcal mol–1 at the CCSD(T) level) with no net activation barrier was initiated by the high-energy isomer of protonated hydroxylamine, which leads to the CH3CONH2+OH isomer. Therefore, the formation of this isomer could be feasible under interstellar conditions from the reaction of the less stable isomer of protonated hydroxylamine and acetic acid. In addition, an analysis of their neutral counterparts, with [H5C2O2N] molecular formula, has been carried out. The relevant spectroscopic parameters for [H6C2O2N]+ and [H5C2O2N] isomers that could help in their laboratory or astronomical detection, by radioastronomy or infrared spectroscopy, are reported.