在稠密天体物理环境中由高能、重和高电荷离子引起的含氨冰的辐解
Radiolysis of ammonia-containing ices by energetic, heavy and highly charged ions inside dense astrophysical environments
摘要：
在致密的分子云和原恒星盘的深处，星际冰受到恒星高能紫外光子的保护。然而，X射线和高能宇宙射线可以穿透这些区域，引发化学反应、分子解离和蒸发过程。我们对重离子、高电荷和高能离子（46 MeV Ni ^[13 +]）与含氨冰的相互作用进行了实验研究，试图模拟在致密天体物理环境中重离子宇宙射线引起的物理化学。测量是在与法国卡昂的重离子加速器GANIL（Grand Accelerateur National d 'Ions Lourds）相连的高真空室中进行的。通过傅里叶变换红外光谱仪（FTIR）在不同的能量密度下进行\textit{In-situ}分析。水、氨和一氧化碳由于重宇宙线离子类似物的离解截面的平均值分别为~ 2 × 10 ^{-13}、1.4 × 10 ^{-13}和1.9 × 10 ^{-13} cm $^2$。在典型的重宇宙射线场存在的情况下，所研究物质的半衰期估计为2-3x10^6年。由重宇宙射线引起的冰压缩（冰塌缩）似乎比由（0.8 MeV）质子引起的冰压缩（冰塌缩）至少高3个数量级。在照射的H2O：NH3：CO冰的情况下，在室温下的红外光谱揭示了五个频带，被暂时分配到振动模式的两性离子甘氨酸（+NH3 CH 2COO-）。
英文摘要：
Deeply inside dense molecular clouds and protostellar disks, the interstellar ices are protected from stellar energetic UV photons. However, X-rays and energetic cosmic rays can penetrate inside these regions triggering chemical reactions, molecular dissociation and evaporation processes. We present experimental studies on the interaction of heavy, highly charged and energetic ions (46 MeV Ni^13+) with ammonia-containing ices in an attempt to simulate the physical chemistry induced by heavy ion cosmic rays inside dense astrophysical environments. The measurements were performed inside a high vacuum chamber coupled to the heavy ion accelerator GANIL (Grand Accelerateur National d'Ions Lourds) in Caen, France.\textit{In-situ} analysis is performed by a Fourier transform infrared spectrometer (FTIR) at different fluences. The averaged values for the dissociation cross section of water, ammonia and carbon monoxide due to heavy cosmic ray ion analogs are ~2x10^{-13}, 1.4x10^{-13} and 1.9x10^{-13} cm$^2$, respectively. In the presence of a typical heavy cosmic ray field, the estimated half life for the studied species is 2-3x10^6 years. The ice compaction (micropore collapse) due to heavy cosmic rays seems to be at least 3 orders of magnitude higher than the one promoted by (0.8 MeV) protons . In the case of the irradiated H2O:NH3:CO ice, the infrared spectrum at room temperature reveals five bands that were tentatively assigned to vibration modes of the zwitterionic glycine (+NH3CH2COO-).
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