Predictions of gas-phase methanimine (CH2NH) abundance in cold cores

Abstract

ABSTRACT Since the 1930s, more than 250 molecules have been discovered in the interstellar medium. With the development of more sensitive telescopes, we keep detecting new more complex species. Amongst them, methanimine (CH2NH) is considered as a pre-biotic molecule as it can be involved in the synthesis of glycine through aminoacetonitrile. CH2NH has been observed in a variety of interstellar sources (hot cores, circumstellar envelops, external galaxies, and even cold cores). We studied the chemistry of this species at low temperature as previous models failed at reproducing the observed abundance in cold cores. First, using the public version of the gas-grain model nautilus (called pnautilus), we tested the effect of new proposed reactions for the production and destruction for CH2NH from the literature. These reactions, in particular association reactions with atomic hydrogen, increases the gas-phase production of CH2NH to a level in disagreement with the published observed values, putting some doubts on these reactions. Using the KIDA gas-phase network, we studied the sensitivity of the CH2NH gas-phase abundance to temperature, density, visual extinction, and cosmic-ray ionization rate. We show that under typical cold core conditions (10 K, 2 × 104 cm−3), CH2NH is formed on the surface of the grains but also from dissociative recombination of protonated ions in the gas. With this model, we are able to reproduce the level of detections in the cold cores Ori-3N and L183.