The methodology employed in this work involves the theoretical characterization and determination of the corresponding global/local potential energy surfaces (PESs) of the target molecules. PESs describe the potential energy of a system in terms of the relative positions of the atoms that make up this system. Inevitably, such potentials carry precise information about the underlying species and are important tools for the analysis of structural isomers, spectroscopy, and reaction dynamics (the main envisaged outcomes of this work). The first step in constructing PESs consists of performing electronic structure calculations for a comprehensive set of nuclear configurations. Obviously, the accuracy of the final potentials hinges on the quality of the quantum-mechanical model so employed. In this work, we aim to employ state-of-the-art ab initio methodologies to obtain PESs with unprecedented accuracy.
The final project results can be summarized as follows: (i) our theoretical calculations predicted a strong enhancement of 13C12C in space and, following an astronomical study, this molecule has first been detected in the interstellar medium (ISM); (ii). we delivered a quantum-chemistry protocol to calculate high-fidelity spectroscopic data of small radicals; (iii). this method was benchmarked against C2O and used to obtain microwave and infrared signatures of C2N-, a potentially important interstellar anion with hitherto no reliable spectroscopic data; (iii). we developed a theoretical methodology to obtain global PESs that are commended for both spectroscopic and reaction dynamics studies; (iv). we applied this method to SiC2 and, from the final PES, reported theoretical thermal rate constants for C2+Si→SiC+C, showing that this reaction may be key to SiC dust formation in high-temperature astronomical environments; (v). we conducted pioneering studies on the C2S molecule and on the C2+S→CS+C reaction dynamics/kinetics which is of primary relevance to interstellar sulfur chemistry and CS formation in space (this study is currently in progress).
Training deliverables included an appropriate knowledge of interstellar chemistry, familiarity with experimental methods and tools, improvement in supervision and management skills, and familiarity with astronomical observations. The project dissemination deliverables were: (i) three published papers, one manuscript submitted and 2 other papers in progress; (ii). presentations of results in 6 international conferences and 12 group meetings at institutes within Europe; (iii). supervision/mentoring of 2 students, transferring my knowledge in theoretical chemistry and astrochemistry acquired during this fellowship. The career development deliverables included completion of several training courses and interaction with a Leiden job coach. The final deliverables concerned with the project management were the contract/project close-out and a risk register.
There is significant potential for exploitation of the project results. From the theoretical perspective, the quantum-chemistry protocols put forth herein will both serve as stand alone general methodologies to be applied to other astronomically relevant radicals or as grounds for further development. In terms of the astrochemical implications, the full set of computed properties for C2N- will aid in high-resolution laboratory experiments and astronomical observations on this peculiar, yet important, molecule. If confirmed, the existence of this species in space will certainly defy our current understanding of interstellar anion chemistry. In turn, the calculated rate coefficients for the 13C+12C2→13C12C+12C, C2+Si→SiC+C, C2+S→CS+C reactions will be implemented (under the form of appropriate Arrhenius-Kooij formulas) in astrophysical and astrochemical reaction network codes. They are all expected to have a profound impact and key importance in several (hot) topics in astrochemistry such as carbon isotopic fractionation (13C+12C2), SiC dust grain formation in inner envelopes surrounding late-type carbon-rich stars (C2+Si) and sulfur chemistry (C2+S).
