Preparation of methanediamine (CH ₂ (NH ₂ ) ₂ )—A precursor to nucleobases in the interstellar medium

Abstract

Although methanediamine (CH 2 (NH 2 ) 2 ) has historically been the subject of theoretical scrutiny, it has never been isolated to date. Here, we report the preparation of methanediamine (CH 2 (NH 2 ) 2 )—the simplest diamine. Low-temperature interstellar analog ices composed of ammonia and methylamine were exposed to energetic electrons which act as proxies for secondary electrons produced in the track of galactic cosmic rays. These experimental conditions, which simulate the conditions within cold molecular clouds, result in radical formation and initiate aminomethyl (ĊH 2 NH 2 ) and amino ( N . H 2 ) radical chemistry. Exploiting tunable photoionization reflectron time-of-flight mass spectrometry (PI-ReToF-MS) to make isomer-specific assignments, methanediamine was identified in the gas phase upon sublimation, while its isomer methylhydrazine (CH 3 NHNH 2 ) was not observed. The molecular formula was confirmed to be CH 6 N 2 through the use of isotopically labeled reactants. Methanediamine is the simplest molecule to contain the NCN moiety and could be a vital intermediate in the abiotic formation of heterocyclic and aromatic systems such as nucleobases, which all contain the NCN moiety.

Quantum Chemistry and Astrochemistry: A Match Made in the Heavens

“…The oft-vaunted “chemical accuracy” of sub-1.0 kcal mol –1 or, even better for non-Americans, sub-1.0 kJ mol –1 has been well-surpassed in quantum chemistry largely since the advent of coupled cluster theory within its singles, doubles, and perturbative triples [CCSD­(T)] incarnation more than 30 years ago. − This is especially true in collusion with correlation consistent basis sets , labeling CCSD­(T)/aug-cc-pVTZ as the “gold standard” of quantum chemistry . Again, application to gas phase or nearly truly isolated chemical reactions like those in the ISM is a perfect fit rendering reaction profiles computed at this level quantitatively insightful. , Additionally, other observables such as ionization potentials and relative energies are readily produced to within 1% or better of experiment which is good enough to compare to observations from a controlled laboratory environment. ,, The advent of explicit correlation in the F12 variants − has allowed triple-ζ-level basis sets to function as quintuple-ζ basis sets precluding the need for costly complete basis set extrapolations in determining such observables to “chemical accuracy,” whether defined by the user as 1.0 kcal mol –1 or 1.0 kJ mol –1 . , Even CCSD­(T)-F12b/cc-pVTZ-F12 single point energies upon DFT optimized geometries for larger molecules are more than accurate enough for clear correlation between theory and experiment for simulated astrochemical conditions . Hence, modern quantum chemistry provides sufficient accuracy for direct correlation to any gas phase physical observable, whether for astrochemical applications or otherwise, where accuracies are needed on the sub-1.0 kJ mol –1 level.…”

“…39,47,48 The advent of explicit correlation in the F12 variants 49−51 has allowed triple-ζlevel basis sets to function as quintuple-ζ basis sets 52 precluding the need for costly complete basis set extrapolations in determining such observables to "chemical accuracy," whether defined by the user as 1.0 kcal mol −1 or 1.0 kJ mol −1 . 53,54 Even CCSD(T)-F12b/cc-pVTZ-F12 single point energies upon DFT optimized geometries for larger molecules are more than accurate enough for clear correlation between theory and experiment for simulated astrochemical conditions. 55 Hence, modern quantum chemistry provides sufficient accuracy for direct correlation to any gas phase physical observable, whether for astrochemical applications or otherwise, where accuracies are needed on the sub-1.0 kJ mol −1 level.…”

pbqff: Push-Button Quartic Force Fields

“…Returning to the example of cyclopropenylidene, the initial HFF requires only 171 points compared to the 1585 points for the normal coordinate QFF, giving a ratio of about 11%. For a C 2 v , nine-atom molecule [CH 2 (NH 2 ) 2 ] the ratio is 742 to 71769, or down to about 1%. Hence, the cost diminishes for the types of large molecules to which these coordinates will be applied.…”

The fundamental vibrational frequencies and spectroscopic constants of the C2O2H2 isomers: molecules known in simulated interstellar ice analogues

“…As such, the present work will fill in the knowledge gap for these molecules and will provide accurate spectroscopic classification for the five lowest-energy, C 2 O 2 H 2 isomers in a manner similar to that for ethynol, 22,28 methanediol, 16,29,30 and diaminomethane. 31,32 The existence of the trans-glyoxal gas phase, experimental fundamental vibrational frequencies will allow for benchmarking of the employed quantum chemical methods, and such findings will give clear error expectations for the fundamental frequencies and spectroscopic constants for the other computed isomers. The present approach in this work will employ the venerable quartic force field (QFF) for approximating the anharmonic potential about the minimum and will be conjoined to second-order rotational and vibrational perturbation theory (VPT2).…”