After decades of searching, astronomers have recently identified specific Polycyclic Aromatic Hydrocarbons (PAHs) in space. Remarkably, the observed abundance of cyanonaphthalene (CNN, C₁₀H₇CN) 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.

经过数十年的探索，天文学家最近在太空中发现了特定的多环芳烃 (PAH)。值得注意的是，在金牛座分子云 (TMC-1) 中观察到的氰萘 (CNN, C ₁₀ H ₇ CN) 丰度比天体物理模型预期的丰度高六个数量级。在这里，我们报告了阳离子形式的 1-CNN 异构体的单分子解离和辐射冷却速率系数。这些结果基于对随时间变化的中性产物发射率和由内部激发的 1-CNN ⁺在类似于星际云的环境中进行研究。我们发现循环荧光——通过热填充电子激发态的辐射弛豫——有效地稳定了 1-CNN ⁺，这是由于通过电子振动耦合大大提高了电子跃迁概率。我们的结果有助于解释 TMC-1 中 CNN 的异常丰度，并挑战被广泛接受的空间中小型多环芳烃快速破坏的观点。