发表机构
RIKEN Cluster for Pioneering Research; Centro de Astrobiología (CAB), CSIC-INTA; LUX, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités; Observatorio Astronómico Nacional (IGN); Observatorio de Yebes (IGN)（RIKEN 前沿研究集群; 天体生物学中心（CAB），CSIC-INTA; 卢米涅实验室，巴黎天文台，PSL 研究大学，CNRS，索邦大学; 国家天文台（IGN）; 耶韦斯天文台（IGN））
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究首次通过GEMS计划观测金牛座分子云中c-C3D2的邻对位比率，发现部分源比率升高，为双氘代分子形成化学模型提供关键基准。
AI 中文摘要
具有相同核的对称分子形成不同的核自旋异构体（邻位和对位），这些异构体无法通过辐射或非弹性跃迁相互转化，从而保留了关于形成条件的线索。在星际介质中，环丙烯亚基（c-C3H2）及其双氘代同位素体（c-C3D2）为研究这些比率提供了理想的实验室。虽然主物种的自旋比率已被测量，但c-C3D2的自旋比率仍无法获得。我们展示了来自GEMS大型计划中三个金牛座分子云源的c-C3D2邻位和对位跃迁的新探测，并重新审视了四个文献中的核心，以首次研究c-C3D2的邻对位比率。使用RADEX结合专门的碰撞速率系数计算柱密度，得出新源的c-C3D2总柱密度为（2.5-5.3）×10^11 cm^-2。推导出的邻对位比率分别为1.5（+0.7-0.6）（B213-C16-1）、1.3（+1.3-0.7）（TMC1-C）和1.0（+1.4-0.7）（TMC1-NH3，统计性）。对于重新审视的源L1544、TMC-1C、TMC-2和L1517B，比率分别为0.4（+0.1-0.1）、0.5（+0.1-0.1）、0.6（+0.2-0.1）和1.4（+0.7-0.5）。总体而言，四个源显示统计性比率，三个源显示较高的非统计性值。这是首次使用详细辐射传输工具对双氘代分子的邻对位比率进行观测确定。某些源中升高的比率可能源于p-D2H+或D3+驱动的反应，并且与H2和c-C3H2的邻对位比率无关。这些发现为研究c-C3D2形成途径的化学模型提供了重要基准。
英文摘要
Symmetric molecules with identical nuclei form distinct nuclear spin isomers (ortho and para) that cannot interconvert via radiative or inelastic transitions, preserving clues about formation conditions. In the interstellar medium, cyclopropenylidene (c-C3H2) and its doubly-deuterated isotopologue (c-C3D2) provide a prime laboratory for studying these ratios. While measured for the main species, spin ratios for c-C3D2 remain unavailable. We present new detections of ortho and para transitions of c-C3D2 toward three Taurus molecular cloud sources from the GEMS Large program, and revisit four literature cores to investigate the para-to-ortho ratio of c-C3D2 for the first time. Column densities were computed using RADEX with dedicated collision rate coefficients, yielding total c-C3D2 column densities of (2.5-5.3) x 10e11 cm-2 for the new sources. The derived para-to-ortho ratios are 1.5(+0.7-0.6) (B213-C16-1), 1.3(+1.3-0.7) (TMC1-C), and 1.0(+1.4-0.7) (TMC1-NH3, statistical). For revisited sources L1544, TMC-1C, TMC-2, and L1517B, ratios are 0.4(+0.1-0.1), 0.5(+0.1-0.1), 0.6(+0.2-0.1), and 1.4(+0.7-0.5), respectively. Overall, four sources show statistical ratios and three show higher non-statistical values. This is the first observational determination of the para-to-ortho ratio in a doubly deuterated molecule using a detailed radiative transfer tool. The elevated ratios in some sources likely stem from p-D2H+ or D3+ driven reactions, and are independent of H2 and c-C3H2 ortho-to-para ratios. These findings offer an essential benchmark for chemical models investigating c-C3D2 formation pathways.
