发表机构
Leiden University; Xinjiang Astronomical Observatory, Chinese Academy of Sciences; Aarhus University（莱顿大学; 中国科学院新疆天文台; 奥胡斯大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究实验量化了不同温度下真空紫外辐照NH$_3$冰生成N$_2$和N$_2$H$_4$的产率，发现15 K时N$_2$产率比25和70 K高约一个数量级，为冷外行星环境N$_2$冰形成提供了新途径。
AI 中文摘要
气体-尘埃天体化学模型预测，在致密核和原行星盘中，大量元素氮以分子氮（N$_2$）形式锁定在气相或冰相中，尽管星际N$_2$冰尚未被直接探测到。罗塞塔号在67P/丘留莫夫-格拉西缅科彗星的测量显示，相对于CO，N$_2$显著贫化，而NH$_3$是探测到的主要含氮冰。我们通过研究NH$_3$冰的温度和通量依赖的真空紫外（VUV）光化学，实验量化了在天文相关条件下NH$_3$冰转化为N$_2$和N$_2$H$_4$的过程。实验在超高真空下进行，使用40单层NH$_3$冰，在15、25和70 K温度下，以115-170 nm波长辐照，总通量为$3.8\ imes10^{18}$光子cm$^{-2}$。采用激光解吸后电离反射式飞行时间质谱（ReTOF-MS）同时监测N$_2$和N$_2$H$_4$。VUV光解有效生成两种产物，其形成动力学和产物比例取决于温度和光子通量。初始生长拟合显示，在15 K时表观冰保留N$_2$形成产率最高，比25和70 K时高约一个数量级。N$_2$/NH$_3$柱密度比作为通量的函数被确定，并与天文约束进行比较。这些结果表明，NH$_3$冰光化学可能为寒冷的外行星环境中N$_2$冰提供额外的形成途径。
英文摘要
Gas--grain astrochemical models predict that a substantial fraction of elemental nitrogen in dense cores and protoplanetary disks is locked in molecular nitrogen (N$_2$), in the gas or ice phase, although interstellar N$_2$ ice has not been directly identified. Rosetta measurements at comet 67P/Churyumov--Gerasimenko showed strong N$_2$ depletion relative to CO, while NH$_3$ was the dominant detected nitrogen-bearing ice. We experimentally quantify the conversion of NH$_3$ ice into N$_2$ and N$_2$H$_4$ under astronomically relevant conditions by studying its temperature- and fluence-dependent VUV photochemistry. Experiments were performed under ultra-high vacuum using 40-monolayer NH$_3$ ice at 15, 25, and 70 K irradiated at 115--170 nm to a total fluence of $3.8\times10^{18}$ photons cm$^{-2}$. Laser desorption with post-ionization reflection time-of-flight mass spectrometry (ReTOF-MS) was used to monitor N$_2$ and N$_2$H$_4$ simultaneously. VUV photolysis efficiently forms both products, with formation kinetics and product ratios depending on temperature and photon fluence. Initial-growth fits gave the highest apparent ice-retained N$_2$ formation yield at 15 K, approximately an order of magnitude above those at 25 and 70 K. The N$_2$/NH$_3$ column-density ratio was determined as a function of fluence and compared with astronomical constraints. These results suggest that NH$_3$ ice photochemistry may provide an additional pathway to N$_2$ ice in cold outer planetary environments.
Comments22 pages, 7 figures
Journal refA&A, 712, A235 (2026)
DOI：10.1051/0004-6361/202658992
