Detection of Interstellar E-1-cyano-1,3-butadiene in GOTHAM Observations of TMC-1

We report the detection of lowest energy conformer $E$-1-cyano-1,3-butadiene ($E$-1-C$_4$H$_5$CN), a linear isomer pyridine, using fourth data reduction GOTHAM deep spectral survey toward TMC-1 with 100 m Green Bank Telescope. performed velocity stacking and matched filter analyses Markov chain Monte Carlo simulations find evidence for presence this molecule at 5.1$\sigma$ level. derive total column density $3.8^{+1.0}_{-0.9}\times 10^{10}$ cm$^{-2}$, which is predominantly found two four components we observe TMC-1. use as proxy constraining gas-phase abundance apolar hydrocarbon 1,3-butadiene. Based on three-phase astrochemical modeling code NAUTILUS an expanded chemical network, our model underestimates cyano-1,3-butadiene by factor 19, peak $2.34 \times 10^{10}\ \mathrm{cm}^{-2}$ Compared to results obtained in previous analyses, 1,3-butadiene increased about orders magnitude. Despite increase, modeled abundances aromatic species do not appear change remain underestimated 1--4 Meanwhile, five-membered ring molecules increase proportionally magnitudes. discuss implications bottom-up formation routes polycyclic molecules.