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
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
