J. Cernicharo, R. Fuentetaja, C. Cabezas, M. Agúndez, N. Marcelino, B. Tercero, J. R. Pardo, and P. de Vicente
reported on the
Discovery of five cyano derivatives of propene with the QUIJOTE line survey
Astron. Astrophys. 663, Art. No. L5 (2022).
The molecular line survey is of the prototypical cold dark molecular cloud TMC-1 and was carried out with the Yebes 40 m radio telescope between 31.0 and 50.4 GHz. 2-Butenenitrile, aka 1-cyanopropene or crotononitrile, was detected in its E (or trans) and Z (or cis) stereoisomeric forms. In addition, 2-propenenitrile, aka 2-cyanopropene or methacrylonitrile was also identified as was 3-butenenitrile, aka 3-cyanopropene or allyl cyanide, in its syn (or cis) and gauche conformers. Please note that while the two 2-butenenitriles are counted as two molecules because conversion requires breaking of a double bond, the 3-butenenitriles are counted as one, even if the rotation around a single bond is at least somewhat hindered at the low temperatures of TMC-1. Several a-type transitions having 4 ≤ J ≤ 8 to 6 ≤ J ≤ 11 and K_a ≤ 2 were identified. A value of T_rot = 7 ± 1 K was derived through rotation diagrams in all instances. The column densities (in units of 10¹⁰ cm⁻²) of the butenenitriles is about 5, 13, 10, 7, and 8 for the E-1-, Z-1-, 2-, syn-3-, and gauche-3-forms, respectively, compared to ~4 × 10¹³ cm⁻² for propene. The combined cyanopropenes are much less abundant in relation to its parent hydrocarbon compared to other detected cyanide derivatives. It is also noteworthy to point out that, unsurprisingly, the abundances among the cyanopropenes do not at all reflect relative energies among these species.

Contributor(s): H. S. P. Müller; 07, 2022; 01, 2024