星际条件下氢和氘在硅酸盐上的粘附系数
Sticking coefficient of hydrogen and deuterium on silicates under interstellar conditions
摘要：
氢和氘原子在星际尘埃颗粒上的吸附是形成分子氢的第一步，而分子氢的形成是星际介质（ISM）中的一个关键反应。在实验和理论上研究了H_2和D_2分子在无定形硅酸盐表面上的粘附系数后，我们将结果外推到原子的粘附系数上，提出了一个计算H_2和D_2分子在硅酸盐和冰尘颗粒上粘附系数的公式。在我们的实验中，我们使用King和Wells方法测量了10 K下H2和D2分子在硅酸盐表面上的粘附系数。它包括在20 K至340 K的温度范围内，用QMS（四极质谱仪）测量样品暴露于分子束期间由表面反射的H2和D2分子的信号。我们测试了一个物理模型的效率，以前开发的坚持在水冰表面。我们将此模型应用到我们的实验结果的H2和D2分子的粘附系数的硅酸盐表面和估计的粘附系数的原子通过一个单一的测量原子复合，并提出了一个外推。H、D、HD、H2和D2在硅酸盐颗粒上的粘附行为与在冰尘颗粒上的相同。粘附随气体温度的升高而减小，并取决于冲击器的质量。表面和撞击物的粘附系数可以用分析公式S（T）来模拟，该公式描述了天体物理学背景下的实验和预期的热分布。参数S0和T0总结在表中。以前的估计H原子的粘附系数接近新的估计，然而，我们发现，当同位素效应被考虑在内，粘附系数的变化可以高达2的因子在T = 100 K。
英文摘要：
Sticking of H and D atoms on interstellar dust grains is the first step in molecular hydrogen formation, which is a key reaction in the InterStellar Medium (ISM). After studying the sticking coefficients of H2 and D2 molecules on amorphous silicate surfaces experimentally and theoretically, we extrapolate the results to the sticking coefficient of atoms and propose a formulae that gives the sticking coefficients of H and D on both silicates and icy dust grains. In our experiments, we used the King and Wells method for measuring the sticking coefficients of H2 and D2 molecules on a silicate surface held at 10 K. It consists of measuring with a QMS (quadrupole mass spectrometer) the signals of H2 and D2 molecules reflected by the surface during the exposure of the sample to the molecular beam at a temperature ranging from 20 K to 340 K. We tested the efficiency of a physical model, developed previously for sticking on water-ice surfaces. We applied this model to our experimental results for the sticking coefficients of H2 and D2 molecules on a silicate surface and estimated the sticking coefficient of atoms by a single measurement of atomic recombination and propose an extrapolation. Sticking of H, D, HD, H2, and D2 on silicates grains behaves the same as on icy dust grains. The sticking decreases with the gas temperature, and is dependent on the mass of the impactor. The sticking coefficient for both surfaces and impactors can be modeled by an analytical formulae S(T), which describes both the experiments and the thermal distribution expected in an astrophysical context. The parameters S0 and T0 are summarized in a table. Previous estimates for the sticking coefficient of H atoms are close to the new estimation; however, we find that, when isotopic effects are taken into account, the sticking coefficient variations can be as much as a factor of 2 at T=100 K.
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