Department of Physics, Stockholm University, Stockholm, Sweden.
School of Chemistry, University of East Anglia, Norwich, United Kingdom.
Nat Commun. 2023 Jan 24;14(1):395. doi: 10.1038/s41467-023-36092-0.
After decades of searching, astronomers have recently identified specific Polycyclic Aromatic Hydrocarbons (PAHs) in space. Remarkably, the observed abundance of cyanonaphthalene (CNN, CHCN) in the Taurus Molecular Cloud (TMC-1) is six orders of magnitude higher than expected from astrophysical modeling. Here, we report unimolecular dissociation and radiative cooling rate coefficients of the 1-CNN isomer in its cationic form. These results are based on measurements of the time-dependent neutral product emission rate and kinetic energy release distributions produced from an ensemble of internally excited 1-CNN studied in an environment similar to that in interstellar clouds. We find that Recurrent Fluorescence - radiative relaxation via thermally populated electronic excited states - efficiently stabilizes 1-CNN, owing to a large enhancement of the electronic transition probability by vibronic coupling. Our results help explain the anomalous abundance of CNN in TMC-1 and challenge the widely accepted picture of rapid destruction of small PAHs in space.
经过几十年的探索，天文学家最近在太空中确定了特定的多环芳烃 (PAHs)。值得注意的是，在金牛座分子云 (TMC-1) 中观测到的氰萘 (CNN，CHCN) 的丰度比天体物理模型预期的高出六个数量级。在这里，我们报告了其阳离子形式的 1-CNN 异构体的单分子离解和辐射冷却速率系数。这些结果基于对一组内部激发的 1-CNN 的时间相关中性产物发射率和动能释放分布的测量，这些 1-CNN 是在类似于星际云环境中研究的。我们发现，由于通过热填充电子激发态的反复荧光 - 辐射弛豫，电子跃迁概率大大增强，从而有效地稳定了 1-CNN。我们的结果有助于解释 TMC-1 中 CNN 的异常丰度，并挑战了空间中小 PAHs 快速破坏的广泛接受的观点。
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