The physics of grain-grain collisions and gas-grain sputtering in interstellar shocks
The physics of grain-grain collisions and gas-grain sputtering in interstellar shocks
复制标题
星际冲击中晶粒碰撞和气体晶粒溅射的物理学
DOI：
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发表时间：
1994
期刊：
影响因子：
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通讯作者：
D. Hollenbach
中科院分区：
文献类型：
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作者：
A. Tielens;C. McKee;C. Seab;D. Hollenbach
粒子间的碰撞和离子溅射会在星际冲击中摧毁尘埃粒子。本文提出了一种分析理论，用于研究颗粒-颗粒碰撞驱动的冲击波在固体中的传播，并与详细的数值计算结果进行了比较。该理论用于确定由颗粒-颗粒碰撞蒸发的颗粒的分数。我们的研究结果预测星际冲击中碰撞颗粒的蒸发比以前的估计少得多。该理论也可用于确定熔化、破碎或经历相变为更高密度相的碰撞颗粒的分数。特别是，后两个过程在星际激波中可能比蒸发更重要。基于大量的实验室研究和理论推导的“普适”溅射关系，对撞击气体离子溅射晶粒进行了重新分析。分析结果进行了比较，石墨/无定形碳，SiO2，SiC，Fe和H2O的溅射可用的实验研究。溅射产额天体物理学相关的材料作为碰撞能量和离子质量的函数。这些产量也平均超过热冲击谱和简单的多项式拟合作为温度的函数，从而产生的产量。导出的溅射产率是相似的，在以前的研究中所采用的，除了石墨附近的阈值，新的产量大得多，由于采用较低的结合能。离子轰击将使星际颗粒的表层非晶化。它还将石墨转化为氢化无定形碳（HAC），深度为10-20 A。这些HAC表面是星际介质中3.4微米吸收特征的载体。
Grain-grain collisions and ion sputtering destroy dust grains in interstellar shocks. An analytical theory is developed for the propagation of shock waves in solids driven by grain-grain collisions, which compares very favorably with detailed numerical calculations. This theory is used to determine the fraction of grain vaporized by a grain-grain collision. Our results predict much less vaporization of colliding grains in interstellar shocks than previous estimates. This theory can also be used to determine the fraction of a colliding grain that melts, shatter, or undergoes a phase transformation to a higher density phase. In particular, the latter two processes can be much more important in interstellar shocks than vaporization. The sputtering of grains by impacting gas ions is reanalyzed based upon extensive laboratory studies and a theoretically derived 'universal'sputtering relation. The analytical results are compared to available experimental studies of sputtering of graphite/amorphous carbon, SiO2, SiC, Fe, and H2O. Sputtering yields for astrophysically relevant materials as a function of impact energy and ion mass are derived. These yields are also averaged over thermal impact spectrum and simple polynomial fits to the resulting yields as a function of temperature are presented. The derived sputtering yields are similar to those adopted in previous studies, except for graphite near threshold where the new yields are much larger due to a lower adopted binding energy. The ion bombardment will amorphitize the surface layers of interstellar grains. It will also convert graphite into hydrogenated amorphous carbon (HAC) to a depth of 10-20 A. It is suggested that these HAC surfaces are the carriers of the 3.4 micrometer absorption feature in the interstellar medium.