Titan的HC $_3$ N、H $^{13}$ CCCN和HCCC $^{15}$ N的干涉成像
Interferometric imaging of Titan's HC$_3$N, H$^{13}$CCCN and HCCC$^{15}$N
摘要：
我们提出了土卫六大气中氰基乙炔同位素的第一张地图，包括H $^{13}$ CCCN和HCCC $^{15}$ N，使用阿塔卡马大型毫米/亚毫米阵列（ALMA）在2017年5月土卫六（南部冬季）至日前后在0.9毫米波段检测到。HC $_3$ N在其$v_7=1$振动激发态的第一个高分辨率地图也被提出，揭示了全球HC $_3$ N分布的独特快照，没有强烈的光学深度效应，对基态（$v=0$）地图产生不利影响。HC PDMATHAMO N的排放被发现在土卫六的南极强烈增强（与北极相比，增加了5.7倍），这与自2015年4月ALMA观测以来，夏季半球HC PDMATHAMO N的快速光化学损失相一致。H $^{13}$ CCCN/HCCC $^{15}$ N通量比在南部HC $_3$ N峰值处导出，并且意味着HC $_3$ N/HCCC $^{15}$ N比为$67\pm14$。这代表了一个显着的富集$^{15}$ N相比，土卫六的主要分子氮水库，其中有一个$^{14}$ N/ $^{15}$ N的比例为167，并证实了光化学的重要性，在确定氮同位素比率在土卫六的有机库存。
英文摘要：
We present the first maps of cyanoacetylene isotopologues in Titan's atmosphere, including H$^{13}$CCCN and HCCC$^{15}$N, detected in the 0.9 mm band using the Atacama Large Millimeter/submillimeter array (ALMA) around the time of Titan's (southern winter) solstice in May 2017. The first high-resolution map of HC$_3$N in its $v_7=1$ vibrationally excited state is also presented, revealing a unique snapshot of the global HC$_3$N distribution, free from the strong optical depth effects that adversely impact the ground-state ($v=0$) map. The HC$_3$N emission is found to be strongly enhanced over Titan's south pole (by a factor of 5.7 compared to the north pole), consistent with rapid photochemical loss of HC$_3$N from the summer hemisphere combined with production and transport to the winter pole since the April 2015 ALMA observations. The H$^{13}$CCCN/HCCC$^{15}$N flux ratio is derived at the southern HC$_3$N peak, and implies an HC$_3$N/HCCC$^{15}$N ratio of $67\pm14$. This represents a significant enrichment in $^{15}$N compared with Titan's main molecular nitrogen reservoir, which has a $^{14}$N/$^{15}$N ratio of 167, and confirms the importance of photochemistry in determining the nitrogen isotopic ratio in Titan's organic inventory.
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