The rich interstellar reservoir of dinitriles: Detection of malononitrile and maleonitrile in TMC-1

• Main Authors: Agundez, M, Bermudez, C, Cabezas, C, Molpeceres, G, Endo, Y, Marcelino, N, Tercero, B, Guillemin, J. -C, de Vicente, P, Cernicharo, J
• Format: Journal Article
• Language: English
• Published: 05-08-2024
• Subjects: Physics - Astrophysics of Galaxies
• DOI: 10.48550/arxiv.2408.02843

While the nitrile group is by far the most prevalent one among interstellar
molecules, the existence of interstellar dinitriles (molecules containing two
-CN groups) has recently been proven. Here we report the discovery of two new
dinitriles in the cold dense cloud TMC-1. These newly identified species are
malononitrile, CH2(CN)2, and maleonitrile, the Z isomer of NC-CH=CH-CN, which
can be seen as the result of substituting two H atoms with two -CN groups in
methane and ethylene, respectively. These two molecules were detected using
data from the ongoing QUIJOTE line survey of TMC-1 that is being carried out
with the Yebes 40m telescope. We derive column densities of 1.8e11 cm-2 and
5.1e10 cm-2 for malononitrile and maleonitrile, respectively. This means that
they are eight and three times less abundant than HCC-CH2-CN and
(E)-HCC-CH=CH-CN, respectively, which are analog molecules detected in TMC-1 in
which one -CN group is converted into a -CCH group. This is in line with
previous findings in which -CCH derivatives are more abundant than the -CN
counterparts in TMC-1. We examined the potential chemical pathways to these two
dinitriles, and we find that while maleonitrile can be efficiently formed
through the reaction of CN with CH2CHCN, the formation of malononitrile is not
clear because the neutral-neutral reactions that could potentially form it are
not feasible under the physical conditions of TMC-1.