The Origin Of The E/Z Isomer Ratio Of Imines In The Interstellar Medium

Optimized geometries of the E, Z and TS stationary points for the three imines considered in this work, and its relative vibrationally adiabatic energies with respect to the less stable isomer (E for cyanomethanimine and propynimine, and Z for ethanimine) in units of kcal/mol.

Recent astronomical observations of both isomers E and Z of imines such as cyanomethanimine, ethanimine and 2-propyn-1-imine, have revealed that the abundances in the ISM of these isomers differ by factors of ~3-10.

Several theories have been proposed to explain the observed behavior, but none of them successfully explains the [E]/[Z] ratios. In this work we present a detailed study of the kinetics of the one-step E-Z isomerization reactions of cyanomethanimine, ethanimine and 2-propyn-1-imine under interstellar conditions (in the 10-400 K temperature range). This reaction was previously thought to be non-viable in the ISM due to its associated high-energy barrier (about 13,000 K). In this Letter, we show that considering the multidimensional small curvature tunneling approximation, the tunneling effect enables the isomerization even at low temperatures.

This is due to the fact that the representative tunneling energy lies in the vibrational ground state of the least stable isomer up to approximately 150 K, making the reaction constants of the isomerization from the least stable to the most stable isomer basically constant. The predicted [E]/[Z] ratios are almost the same as those reported from the astronomical observations for all imines observed. This study demonstrates that the [E]/[Z] ratio of imines in the ISM strongly depends on their relative stability.

Juan García de la Concepción, Izaskun Jiménez-Serra, José Carlos Corchado, Víctor M. Rivilla, Jesús Martín-Pintado

Comments: 13 pages, 2 figures
Subjects: Chemical Physics (physics.chem-ph); Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2104.07913 [physics.chem-ph] (or arXiv:2104.07913v1 [physics.chem-ph] for this version)
Submission history
From: Juan García De La Concepción
[v1] Fri, 16 Apr 2021 06:30:58 UTC (695 KB)
Astrobiology, Astrochemistry,

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