标题： 在金牛TMC-1中星际探测到第二种五元环分子2-氰基环戊二烯C$_5$H$_5$CN 显示英文标题

标题： Interstellar Detection of 2-Cyanocyclopentadiene, C$_5$H$_5$CN, a Second Five-Membered Ring Toward TMC-1

摘要： 利用绿岸望远镜的射电观测，已经在致密云团金牛座分子云-1（TMC-1）中发现了第二个五元环存在的证据。 基于对该源在厘米波段正在进行的大规模、高灵敏度光谱线巡天（GOTHAM）的进一步观测，我们结合了光谱叠加、马尔可夫链蒙特卡洛（MCMC）以及匹配滤波技术，检测到了2-氰基环戊二烯，这是最近在同一方法下在此处发现的1-氰基环戊二烯的一个低能异构体。 新的观测数据还显著提高了更稳定异构体的探测显著性，并在23至32 GHz范围内提供了几个单独跃迁的证据。 通过我们的MCMC分析，我们分别得出了1-氰基环戊二烯和2-氰基环戊二烯的总柱密度，分别为$8.3\times10^{11}$和$1.9\times10^{11}$ cm$^{-2}$，对应的比例为4.4(6)，倾向于前者。 推导出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基化，类似于苯腈的形成方式。 显示英文摘要

摘要： 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 yields 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 total column densities of $8.3\times10^{11}$ and $1.9\times10^{11}$ cm$^{-2}$ for 1- and 2-cyanocyclopentadiene respectively, corresponding to a ratio of 4.4(6) favoring the former. The derived abundance ratios point towards a common formation pathway - most likely being cyanation of cyclopentadiene by analogy to benzonitrile.