Date of Award

6-15-2026

Document Type

Thesis

Degree Name

MSc by Research in Natural Sciences

First Advisor

Dr. Suranjan Shil

Second Advisor

Dr. Shalima Puthiyaveettil

Abstract

Nitrile-substitutedpolycyclic aromatic hydrocarbons (CN-PAHs) are of growing astrochemical interest because they connect aromatic carbon chemistry with the rich nitrile chemistry observed in interstellar environments. Motivated by the recent detection of cyanocoronene (C24H11CN) in Taurus Molecular Cloud- I (TMC-1), this thesis investigates both the possible formation pathways of cyanocoronene and its infrared detectability in astronomical environments. In the first part of the work, several chemically plausible reaction routes were explored using density functional theory (DFT), along with higher-level multireference calculations including CASSCF and NEVPT2 for selected key structures. Geometry optimizations, vibrational frequency calculations, and transition-state searches were carried out to construct the corresponding potential energy surfaces (PES) and compare the relative energetic feasibility of the proposed mechanisms. The results show that the different pathways are not equally favorable under interstellar conditions, and the most efficient route is determined by the lowest overall activation barriers. In the second part of the thesis, the anharmonic infrared spectrum of cyanocoronene was computed and compared with JWST/NIRSpec observations of several PAH-rich astrophysical environments. Special attention was given to the characteristic CN-stretching region near 4.3-4.4 µm, which is expected to contain diagnostic features of nitrile-bearing aromatic molecules. The theoretical spectrum shows strong bands in this region, but the continuum-subtracted JWST data do not reveal any unambiguous CN-PAH feature in the selected sources. The absence of a secure detection is consistent with spec-tral blending, weak intrinsic emission, and limited signal-to-noise in complex astrophysical spectra. Overall, this work provides a combined computational and observational framework for understanding cyanocoronene in the interstellar medium (ISM) and for guiding future searches for CN-PAHs in space.

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