Spectroscopic Constants and Anharmonic Vibrational Frequencies of C(O)OC, c-C2O2 and Their Silicon-Containing Analogues

Comets are likely to contain various carbon oxide molecules potentially including C(O)OC and c-C2O2 on their surfaces and comae, as well as their silicon-substituted analogues possibly playing a role in the formation of interstellar dust grains. In this work, high-level quantum chemical data are provided to support such potential future astrophysical detection through the generation of predicted rovibrational data. Laboratory-based chemistry would also benefit from such aforementioned computational benchmarking considering these molecules' historic computational and experimental elusiveness. Coupled-cluster singles, doubles, and perturbative triples, the F12b formalism, and the cc-pCVTZ-F12 basis set garner the rapid, yet highly trusted F12-TcCR level of theory leveraged presently. This current work points to all four molecules' strong IR activity, coupled with large intensities, thus suggesting the potential for JWST detection. Although Si(O)OSi possesses a permanent dipole moment significantly larger than those of the other molecules of present interest, the significant abundance of the potential precursor carbon monoxide suggests that the dicarbon dioxide molecules may yet be observable in the microwave region of the electromagnetic spectrum. Thus, this present work details the likely existence and detectability of these four cyclic molecules, providing updated implications compared to previous work performed both experimentally and computationally.

Chemistry and physics of dopants embedded in helium droplets

Helium droplets represent a cold inert matrix, free of walls with outstanding properties to grow complexes and clusters at conditions that are perfect to simulate cold and dense regions of the interstellar medium. At sub-Kelvin temperatures, barrierless reactions triggered by radicals or ions have been observed and studied by optical spectroscopy and mass spectrometry. The present review summarizes developments of experimental techniques and methods and recent results they enabled.

How to capture C2O2: structures and bonding of neutral and charged complexes [(NHC)-C2O2-(NHC)]q (NHC = N-heterocyclic carbene; q = 0, 1+, 2+)

We present the results of DFT calculations and a thorough bonding analysis of the neutral and charged complexes of the elusive C₂O₂ species stabilized by two NHC ligands. It is shown that the thermodynamic stability of the neutral complex [(NHC)-C₂O₂-(NHC)] is due to the low-lying triplet state of [NHC-CO] (T), which is only 3.2 kcal mol^-1 higher in energy than the singlet state [NHC-CO] (S), while the triplet state of CO is 131.9 kcal mol^-1 above the singlet. The much lower S/T gap of [NHC-CO] than in CO comes from the charge donation of NHC into the degenerate π* LUMO of CO and the concomitant mixing of the LUMO of NHC with the degenerate π* LUMO of CO, which strongly lowers the energy difference between HOMO and LUMO in the complex. The energy gain resulting from the formation of the CC double bond compensates the singlet-triplet gap and the thermodynamic instability of the fragments [NHC-CO] (S). The dissociation of neutral [(NHC)-C₂O₂-(NHC)] to 2NHC and 2CO molecules is calculated to be endothermic by D_o = 78.2 kcal mol^-1. The bonding analysis indicates that the neutral and the charged molecules [(NHC)-C₂O₂-(NHC)]^q have a central unit with C-C single bonds, where a combination of electron sharing and s dative interactions leads to very strong carbon-carbon bonds complemented by minor π-donation, which make all systems stable with respect to dissociation reactions. The central C₂O₂ fragment carries a large negative partial charge in the neutral and singly charged compounds [(NHC)-C₂O₂-(NHC)]^0,1+, while it is neutral in the dication [(NHC)-C₂O₂-(NHC)]²⁺.

All-nitrogen spiropentadiene-N5. J Chem Phys 2021;155:174304. [PMID: 34742197 DOI: 10.1063/5.0070369] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Of the pentanitrogen cation (N₅ ⁺) family, the only experimentally known isomer is the V-shaped structure 01. Here, we showed that a super-high-energy (∼100 kcal/mol above 01) all-nitrogen spiropentadiene 02 with considerable σ-delocalization deserves pursuit as the first spirocyclic all-nitrogen molecule, at least spectroscopical.