Methanimine as a Key Precursor of Imines in the Interstellar Medium: The Case of Propargylimine

Abstract

A gas-phase formation route is proposed for the recently detected propargylimine molecule. In analogy to other imines, such as cyanomethanimine, the addition of a reactive radical (C 2 H in the present case) to methanimine (CH 2 NH) leads to reaction channels open also in the harsh conditions of the interstellar medium. Three possible isomers can be formed in the CH 2 NH  + C 2 H reaction: Z- and E-propargylimine (Z-,E-PGIM) as well as N-ethynyl-methanimine (N-EMIM). For both PGIM species, the computed global rate coefficient is nearly constant in the 20–300 K temperature range, and of the order of 2–3 ×  10 −10 cm 3 molecule −1 s −1 , while that for N-EMIM is about two orders of magnitude smaller. Assuming equal destruction rates for the two isomers, these results imply an abundance ratio for PGIM of [Z]/[E]  ∼ 1.5, which is only slightly underestimated with respect to the observational datum.