标题： 扩散介导的尘埃颗粒表面反应的扫掠率 显示英文标题

标题： The sweeping rate in diffusion-mediated reactions on dust grain surfaces

摘要： 星际云中一个突出的化学反应是在尘埃颗粒表面通过复合形成分子氢。迄今为止，分析方法建模此类系统时通过采用反应物清除率的简单版本，忽略了问题的空间方面。 我们展示了如何通过一致定义清除率来考虑这些方面，并精确计算出球形颗粒的情况。可以识别出两种情况：小颗粒上两个反应物几乎肯定会相遇，而在大颗粒上这种情况非常不可能发生。 我们将真实的清除率与常规近似值进行比较，发现两种情况下都存在特征性的减少，对于大颗粒尤为明显。 使用二维随机游走分析已知结果，可以直观地理解这些效应。 最后，我们检查了在计算氢复合效率时使用真实清除率的影响：对于固定温度，效率可以大幅降低，相对于此，小颗粒的重要性增加，但复合效率较高的温度窗口没有显著变化。 显示英文摘要

摘要： A prominent chemical reaction in interstellar clouds is the formation of molecular hydrogen by recombination, which essentially takes place on dust grain surfaces. Analytical approaches to model such a system have hitherto neglected the spatial aspects of the problem by employing a simplistic version of the sweeping rate of reactants. We show how these aspects can be accounted for by a consistent definition of the sweeping rate, and calculate it exactly for a spherical grain. Two regimes can be identified: Small grains, on which two reactants almost surely meet, and large grains, where this is very unlikely. We compare the true sweeping rate to the conventional approximation and find a characteristic reduction in both regimes, most pronounced for large grains. These effects can be understood heuristically using known results from the analysis of two-dimensional random walks. We finally examine the influence of using the true sweeping rate in the calculation of the efficiency of hydrogen recombination: For fixed temperature, the efficiency can be reduced considerably, and relative to that, small grains gain in importance, but the temperature window in which recombination is efficient is not changed substantially.