The formation of monosubstituted cyclopropenylidene derivatives in the interstellar medium via neutral-neutral reaction pathways

Five substituted cyclopropenylidene derivatives (c-C3HX, X = CN, OH, F, NH2), all currently undetected in the interstellar medium (ISM), are found herein to have mechanistically viable, gas-phase formation pathways through neutral-neutral additions of ·X onto c-C3H2. The detection and predicted formation mechanism of c-C3HC2H introduces a need for the chemistry of c-C3H2 and any possible derivatives to be more fully explored. Chemically accurate CCSD(T)-F12/cc-pVTZ-F12 calculations provide exothermicities of additions of various radical species to c-C3H2, alongside energies of submerged intermediates that are crossed to result in product formation. Of the novel reaction mechanisms proposed, the addition of the cyano radical is the most exothermic at -16.10 kcal mol-1. All five products are found to or are expected to have at least one means of associating barrierlessly to form a submerged intermediate, a requirement for the cold chemistry of the ISM. The energetically-allowed additions arise as a result of the strong electrophilicity of the radical species as well as the product stability gained through substituent-ring conjugation

Gas-phase formation and spectroscopic characterization of the disubstituted cyclopropenylidenes c-C3(C2H)2, c-C3(CN)2, and c-C3(C2H)(CN)

Aims. The detection of c-C3HC2H and possible future detection of c-C3HCN provide new molecules for reaction chemistry in the dense ISM where R-C2 and R-CN species are prevalent. Determination of chemically viable c-C3HC2H and c-C3HCN derivatives and their prominent spectral features can accelerate potential astrophysical detection for this chemical family. This work will characterize three such derivatives: c-C3(C2H)2, c-C3(CN)2, and c-C3(C2H)(CN). Methods. Interstellar reaction pathways of small carbonaceous species are well-replicated through quantum chemical means. Highly-accurate cc-pVX Z-F12/CCSD(T)-F12 (X =D,T) calculations generate the energetics of chemical formation pathways as well as the basis for quartic force field and second-order vibrational perturbation theory rovibrational analysis of the vibrational frequencies and rotational constants of the molecules under study. Results. The formation of c-C3(C2H)2 is as thermodynamically and, likely, stepwise favorable as the formation of c-C3HC2H, rendering its detectability to be mostly dependent on the concentrations of the reactants. c-C3(C2H)2 and c-C3(C2H)(CN) will be detectable through radioastronomical observation with large dipole moments of 2.84 D and 4.26 D, respectively, while c-C3(CN)2 has an exceedingly small and likely unobservable dipole moment of 0.08 D. The most intense frequency for c-C3(C2H)2 is ν2 at 3316.9 cm−1 (3.01 µm) with an intensity of 140 km mol−1. c-C3(C2H)(CN) has one frequency with a large intensity, ν1, at 3321.0 cm−1 (3.01 µm) with an intensity of 82 km mol−1. c-C3(CN)2 lacks intense vibrational frequencies within the range that current instrumentation can readily observe. Conclusions. c-C3(C2H)2 and c-C3(C2H)(CN) are viable candidates for astrophysical observation with favorable reaction profiles and spectral data produced herein, but c-C3(CN)2 will not be directly observable through any currently-available remote sensing means even if it forms in large abundances

Formation and Destruction of Si₆O₁₂ Nanostructures in the Gas Phase: Applications to Grain Nucleation and Water Generation

Silica grains are ubiquitous in both circumstellar media and rocky bodies and are vital to cosmic chemical processes, such as surface-catalyzed reactions and lunar water generation. Despite their pervasiveness, the chemical processes behind their formation and destruction, both of which are key to understanding their broader chemistry, are not fully established as of yet. Using chemically accurate CCSD(T)-F12/cc-pVTZ-F12 quantum chemical calculations, a reaction pathway including the possible bulk silica precursors Si3O6 and Si6O12 is mapped out herein. Through the reaction of SiO and H2O, the formation of such precursors is possible under circumstellar conditions. Expansion of this pathway may contribute to a complete understanding of silica and silicate chemistry throughout the universe. The constructed reaction pathway also shows that in the reverse reaction, processing of lunar silicates under the available photon flux of the sun can result in H2O production, following previous observations. The acceleration of H2O generation may be made possible through exposure of lunar silica to applied H2 in future aerospace ventures

Gas-phase formation and spectroscopic characterization of the disubstituted cyclopropenylidenes

Aims. The detection of c-C3HC2H and possible future detection of c-C3HCN provide new molecules for reaction chemistry in the dense interstellar medium (ISM) where R-C2H and R-CN species are prevalent. Determination of chemically viable c-C3HC2H and c-C3HCN derivatives and their prominent spectral features can accelerate potential astrophysical detection of this chemical family. This work characterizes three such derivatives: c-C3(C2H)2, c-C3(CN)2, and c-C3(C2H)(CN). Methods. Interstellar reaction pathways of small carbonaceous species are well replicated through quantum chemical means. Highly accurate cc-pVXZ-F12/CCSD(T)-F12 (X = D,T) calculations generate the energetics of chemical formation pathways as well as the basis for quartic force field and second-order vibrational perturbation theory rovibrational analysis of the vibrational frequencies and rotational constants of the molecules under study. Results. The formation of c-C3(C2H)2 is as thermodynamically and, likely, as stepwise favorable as the formation of c-C3HC2H, rendering its detectability to be mostly dependent on the concentrations of the reactants. Both c-C3(C2H)2 and c-C3(C2H)(CN) will be detectable through radioastronomical observation with large dipole moments of 2.84 D and 4.26 D, respectively, while c-C3(CN)2 has an exceedingly small and likely unobservable dipole moment of 0.08 D. The most intense frequency for c-C3(C2H)2 is v2 at 3316.9 cm–1 (3.01 μm), with an intensity of 140 km mol–1. The mixed-substituent molecule c-C3(C2H)(CN) has one frequency with a large intensity, v1, at 3321.0 cm–1 (3.01 μm), with an intensity of 82 km mol–1. The molecule c-C3(CN)2 lacks intense vibrational frequencies within the range that current instrumentation can readily observe. Conclusions. Both c-C3(C2H)2 and c-C3(C2H)(CN) are viable candidates for astrophysical observation, with favorable reaction profiles and spectral data produced herein, but c-C3(CN)2 will not be directly observable through any currently available remote sensing means, even if it forms in large abundances