Using radio observations with the Green Bank Telescope, evidence has now been found for a second five-membered ring in the dense cloud Taurus Molecular Cloud-1 (TMC-1). Based on additional observations of an ongoing, large-scale, high-sensitivity spectral line survey (GOTHAM) at centimeter wavelengths toward this source, we have used a combination of spectral stacking, Markov Chain Monte Carlo (MCMC), and matched filtering techniques to detect 2-cyanocyclopentadiene, a low-lying isomer of 1-cyanocyclopentadiene, which was recently discovered there by the same methods. The new observational data also yield a considerably improved detection significance for the more stable isomer and evidence for several individual transitions between 23–32 GHz. Through our MCMC analysis, we derive cospatial, total column densities of 8.3 10¹¹ and 1.9 10¹¹ cm⁻² for 1- and 2-cyanocyclopentadiene, respectively, corresponding to a ratio of ∼4.4 favoring the former. The derived abundance ratios point toward a common formation pathway—most likely being cyanation of cyclopentadiene by analogy to benzonitrile.

使用绿岸望远镜的无线电观测，现在已经发现了在密集云金牛座分子云 1 (TMC-1) 中存在第二个五元环的证据。基于对该光源的厘米波长正在进行的大规模高灵敏度谱线调查 (GOTHAM) 的额外观察，我们结合使用了光谱叠加、马尔可夫链蒙特卡罗 (MCMC) 和匹配滤波技术来检测 2-氰基环戊二烯，一种 1-氰基环戊二烯的低位异构体，最近通过相同的方法在那里发现。新的观测数据还为更稳定的异构体提供了显着改善的检测意义，并提供了 23-32 GHz 之间几个单独跃迁的证据。通过我们的 MCMC 分析，我们推导出 8.3 10 的共空间总列密度1- 和 2- 氰基环戊二烯分别为¹¹和 1.9 10 ¹¹ cm ^-2，对应于约 4.4 的比率有利于前者。衍生的丰度比指向一个共同的形成途径——最有可能是环戊二烯的氰化，类似于苄腈。