Herbst Eric, Cuppen Herma M
Department of Physics, Ohio State University, Columbus, OH 43210, USA.
Proc Natl Acad Sci U S A. 2006 Aug 15;103(33):12257-62. doi: 10.1073/pnas.0601556103. Epub 2006 Aug 7.
Although still poorly understood, the chemistry that occurs on the surfaces of interstellar dust particles profoundly affects the growth of molecules in the interstellar medium. The most important surface reaction is the conversion of atomic to molecular hydrogen, which is a precursor for all subsequent molecular development and which occurs both in diffuse and dense interstellar clouds. Another set of surface reactions produces icy mantles of many monolayers in cold and dense regions of the interstellar medium. The monolayers are dominated by water ice but also contain CO, CO(2), and occasionally methanol. In this work, we first review both our stochastic approach to the surface chemistry that can occur on small dust particles and how it has been applied to the problem of the formation of molecular hydrogen. This latter problem is strongly affected by the pulsed heating of smaller grains by photons. Photons are not the only source of pulsed heating; cosmic rays also can heat interstellar grains in a pulsed manner. Here, we calculate the heating by cosmic rays for different grain sizes and cosmic ray components. It is then shown that this mechanism is an important one for desorption of ice mantles.
尽管仍未被充分理解，但星际尘埃颗粒表面发生的化学反应深刻影响着星际介质中分子的生长。最重要的表面反应是原子氢向分子氢的转化，这是所有后续分子发展的前身，且在弥漫和致密的星际云中都会发生。另一组表面反应在星际介质的寒冷致密区域产生许多单层的冰质覆盖层。这些单层主要由水冰构成，但也包含一氧化碳、二氧化碳，偶尔还有甲醇。在这项工作中，我们首先回顾我们针对小尘埃颗粒表面可能发生的化学过程所采用的随机方法，以及该方法如何应用于分子氢形成问题。后一个问题受到光子对较小颗粒的脉冲加热的强烈影响。光子并非脉冲加热的唯一来源；宇宙射线也能以脉冲方式加热星际颗粒。在此，我们计算了不同颗粒尺寸和宇宙射线成分下宇宙射线的加热情况。结果表明，这种机制对于冰质覆盖层的解吸是一个重要机制。
