Discovery of Interstellar 2-Cyanoindene (2-C₉H₇CN) in GOTHAM Observations of TMC-1

Abstract We present laboratory rotational spectroscopy of five isomers cyanoindene (2-, 4-, 5-, 6-, and 7-cyanoindene) using a cavity Fourier transform microwave spectrometer operating between 6 40 GHz. Based on these measurements, we report the detection 2-cyanoindene (1H-indene-2-carbonitrile; 2- C 9 mathvariant="normal">H 7 CN ) in GOTHAM line survey observations dark molecular cloud TMC-1 Green Bank Telescope at centimeter wavelengths. Using combination Markov Chain Monte Carlo, spectral stacking, matched filtering techniques, find evidence for presence this molecule 6.3 σ level. This provides first direct observation ratio cyano-substituted polycyclic aromatic hydrocarbon to its pure counterpart, case indene, same source. discuss possible formation chemistry species, including why have only detected one TMC-1. then examine overall hydrocarbon:CN-substituted across other simpler as well compare those ratios predicted by astrochemical models. conclude that while models are not yet sufficiently accurate reproduce absolute abundances they do good job predicting further solidifying -CN tagged species excellent proxies their fully symmetric counterparts.