A theoretical investigation of the reaction between the amidogen, NH, and the ethyl, C2H5, radicals: a possible gas-phase formation route of interstellar and planetary ethanimine

TL;DR

This study uses electronic structure and kinetic calculations to explore the NH and C2H5 radical reaction, revealing a fast process mainly producing methanimine and methyl radicals, with implications for interstellar chemistry.

Contribution

It provides a detailed theoretical analysis of the NH + C2H5 reaction, estimating rate coefficients, product ratios, and exploring its role in forming ethanimine in space.

Findings

Reaction is very fast, near gas-kinetics limit.

Main product is methanimine and methyl radical (~86-88%).

E- and Z-ethanimine are minor products (~5-7%).

Abstract

The reaction between the amidogen, NH, radical and the ethyl, C2H5, radical has been investigated by performing electronic structure calculations of the underlying doublet potential energy surface. Rate coefficients and product branching ratios have also been estimated by combining capture and RRKM calculations. According to our results, the reaction is very fast, close to the gas-kinetics limit. However, the main product channel, with a yield of ca. 86-88% in the range of temperatures investigated, is the one leading to methanimine and the methyl radical. The channels leading to the two E-, Z- stereoisomers of ethanimine account only for ca. 5-7% each. The resulting ratio [E-CH3CHNH]/[Z-CH3CHNH] is ca. 1.2, that is a value rather lower than that determined in the Green Bank Telescope PRIMOS radio astronomy survey spectra of Sagittarius B2 North (ca. 3). Considering that ice chemistry would produce essentially only the most stable isomer, a possible conclusion is that the observed [E-CH3CHNH]/[Z-CH3CHNH] ratio is compatible with a combination of gas-phase and grain chemistry. More observational and laboratory data are needed to definitely address this issue.