分子在无孔无定形水冰上的粘附
Sticking of molecules on non-porous amorphous water ice
摘要：
要精确模拟星际介质的物理和化学过程，就需要详细了解原子和分子如何吸附在尘埃颗粒上。然而，粘附系数是一个介于0和1之间的数字，它测量粒子与表面相互作用的第一步，通常在ISM环境的模拟中假设为0.5或1。本文报道了H $_2$、D $_2$、N $_2$、O $_2$、CO、CH $_4$和CO $_2$在无孔非晶态固体水（np-ASW）上的粘附系数的测定。粘附系数的测量在很宽的表面温度范围内使用高度准直的分子束。我们发现，标准的方法测量的粘附系数-国王-威尔斯方法-导致低估的捕获事件，其中有不完全的能量调节的分子在表面上。使用脉冲分子束的表面散射实验，而不是用来测量粘附系数。基于实测的粘附系数值，我们提出了一个有用的粘附系数作为晶粒温度和分子表面结合能的函数的一般公式。我们使用这个公式在ISM气体-颗粒化学的模拟中找到粘附对颗粒和气相中关键分子丰度的影响。
英文摘要：
Accurate modeling of physical and chemical processes in the interstellar medium requires detailed knowledge of how atoms and molecule adsorb on dust grains. However, the sticking coefficient, a number between 0 and 1 that measures the first step in the interaction of a particle with a surface, is usually assumed in simulations of ISM environments to be either 0.5 or 1. Here we report on the determination of the sticking coefficient of H$_2$, D$_2$, N$_2$, O$_2$, CO, CH$_4$, and CO$_2$ on non-porous amorphous solid water (np-ASW). The sticking coefficient was measured over a wide range of surface temperatures using a highly collimated molecular beam. We showed that the standard way of measuring the sticking coefficient --- the King-Wells method --- leads to the underestimation of trapping events in which there is incomplete energy accommodation of the molecule on the surface. Surface scattering experiments with the use of a pulsed molecular beam are used instead to measure the sticking coefficient. Based on the values of the measured sticking coefficient we suggest a useful general formula of the sticking coefficient as a function of grain temperature and molecule-surface binding energy. We use this formula in a simulation of ISM gas-grain chemistry to find the effect of sticking on the abundance of key molecules both on grains and in the gas-phase.
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