TMC-1中的枯烯卡宾：$l$ $_2$ C $_5$的天文发现
Cumulene carbenes in TMC-1: Astronomical discovery of $l$-H$_2$C$_5$
摘要：
我们报告了在空间中首次探测到的累积多烯碳链$l$ -H $_2$ C $_5$ .使用Yebes 40米射电望远镜在31.0-50.4 GHz范围内探测到TMC-1的11个转动跃迁，其中$J_{up}$ = 7-10，$K_a$ = 0和1。我们推导出（1.8 $\pm$ 0.5）$\times$ 10 $^{10}$ cm $^{-2}$的柱密度。此外，我们报告的其他cumulene卡宾以前在TMC-1中检测到的观察，比较它们的丰度与新检测到的cumulene卡宾链。我们发现$l$-H $_2$ C $_5$的丰度比较大的累积烯卡宾$l$-H $_2$ C $_6$低$\sim$ 4.0倍，而它的丰度比较短链的$l$-H $_2$ C $_3$和$l$-H $_2$ C $_4$低$\sim$ 300倍和$\sim$ 500倍.我们讨论了TMC-1中这些累积多烯最可能的气相化学途径，并强调需要化学动力学研究能够区分不同的异构体，以阐明C $_n$ H $_2$异构体与$n$ \，$>$\，3的化学。
英文摘要：
We report the first detection in space of the cumulene carbon chain $l$-H$_2$C$_5$. A total of eleven rotational transitions, with $J_{up}$ = 7-10 and $K_a$ = 0 and 1, were detected in TMC-1 in the 31.0-50.4 GHz range using the Yebes 40m radio telescope. We derive a column density of (1.8$\pm$0.5)$\times$10$^{10}$ cm$^{-2}$. In addition, we report observations of other cumulene carbenes detected previously in TMC-1, to compare their abundances with the newly detected cumulene carbene chain. We find that $l$-H$_2$C$_5$ is $\sim$4.0 times less abundant than the larger cumulene carbene $l$-H$_2$C$_6$, while it is $\sim$300 and $\sim$500 times less abundant than the shorter chains $l$-H$_2$C$_3$ and $l$-H$_2$C$_4$. We discuss the most likely gas-phase chemical routes to these cumulenes in TMC-1 and stress that chemical kinetics studies able to distinguish between different isomers are needed to shed light on the chemistry of C$_n$H$_2$ isomers with $n$\,$>$\,3.
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