Faraday Discuss. 2014;168:267-85. doi: 10.1039/c3fd00132f.
The effect of UV photon (120-200 nm) and electron (2 keV) irradiation of analogues of interstellar carbonaceous dust and of glycine were investigated by means of IR spectroscopy. Films of hydrogenated amorphous carbon (HAC), taken as dust analogues, were found to be stable under UV photon and electron bombardment. High fluences of photons and electrons, of the order of 10(19) cm(-2), were needed for a film depletion of a few percent. UV photons were energetically more effective than electrons for depletion and led to a certain dehydrogenation of the HAC samples, whereas electrons led seemingly to a gradual erosion with no appreciable changes in the hydrocarbon structure. The rates of change observed may be relevant over the lifetime of a diffuse cloud, but cannot account for the rapid changes in hydrocarbon IR bands during the evolution of some proto-planetary nebulae. Glycine samples under the same photon and electron fluxes decay at a much faster rate, but tend usually to an equilibrium value different from zero, especially at low temperatures. Reversible reactions re-forming glycine, or the build-up of less transparent products, could explain this behavior. CO2 and methylamine were identified as UV photoproducts. Electron irradiation led to a gradual disappearance of the glycine layers, also with formation of CO2. No other reaction products were clearly identified. The thicker glycine layers (a few hundred nm) were not wholly depleted, but a film of the order of the electron penetration depth (80 nm), was totally destroyed with an electron fluence of -1 x 10(18) cm(-2). A 60 nm ice layer on top of glycine provided only partial shielding from the 2 keV electrons. From an energetic point of view, 2 keV electrons are less efficient than UV photons and, according to literature data, much less efficient than MeV protons for the destruction of glycine. The use of keV electrons to simulate effects of cosmic rays on analogues of interstellar grains should be taken with care, due to the low penetration depths of electrons in many samples of interest.
通过红外光谱法研究了模拟星际碳质尘埃和甘氨酸的紫外线光子（120-200nm）和电子（2keV）辐照的影响。将氢化非晶碳（HAC）薄膜作为尘埃模拟物，发现它们在紫外线光子和电子轰击下稳定。需要高达 10（19）cm（-2）的高光子和电子通量才能使薄膜损耗几个百分点。对于 HAC 样品的损耗，紫外线光子比电子更有效，并导致 HAC 样品的一定程度的脱氢，而电子似乎导致逐渐侵蚀，烃结构没有明显变化。观察到的变化率可能与弥漫云的寿命有关，但不能解释某些原行星状星云演化过程中烃类 IR 带的快速变化。在相同的光子和电子通量下，甘氨酸样品的衰减速度要快得多，但通常趋于不同于零的平衡值，尤其是在低温下。可重新形成甘氨酸的可逆反应，或形成不透明产物的积累，可能解释这种行为。鉴定出 CO2 和甲胺是紫外线光产物。电子辐照导致甘氨酸层逐渐消失，同时形成 CO2。没有明确识别出其他反应产物。较厚的甘氨酸层（几百纳米）没有完全耗尽，但电子通量为-1 x 10（18）cm（-2）时，电子穿透深度（80nm）量级的薄膜完全被破坏。甘氨酸顶部的 60nm 冰层仅提供部分屏蔽，以防止 2keV 电子穿透。从能量的角度来看，2keV 电子的效率不如紫外线光子，并且根据文献数据，对于甘氨酸的破坏，其效率远低于 MeV 质子。由于许多感兴趣的样品中的电子穿透深度较低，因此应谨慎使用 keV 电子模拟宇宙射线对星际颗粒类似物的影响。
