School of Chemistry, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK.
Nat Chem. 2013 Sep;5(9):745-9. doi: 10.1038/nchem.1692. Epub 2013 Jun 30.
Understanding the abundances of molecules in dense interstellar clouds requires knowledge of the rates of gas-phase reactions between uncharged species. However, because of the low temperatures within these clouds, reactions with an activation barrier were considered too slow to play an important role. Here we show that, despite the presence of a barrier, the rate coefficient for the reaction between the hydroxyl radical (OH) and methanol--one of the most abundant organic molecules in space--is almost two orders of magnitude larger at 63 K than previously measured at ∼200 K. We also observe the formation of the methoxy radical product, which was recently detected in space. These results are interpreted by the formation of a hydrogen-bonded complex that is sufficiently long-lived to undergo quantum-mechanical tunnelling to form products. We postulate that this tunnelling mechanism for the oxidation of organic molecules by OH is widespread in low-temperature interstellar environments.
要了解密集星际云内分子的丰度，需要了解未带电物种之间气相反应的速率。然而，由于这些云内的低温，带有激活势垒的反应被认为太慢而无法发挥重要作用。在这里，我们表明，尽管存在势垒，但羟基自由基 (OH) 和甲醇之间的反应速率系数——在太空中最丰富的有机分子之一——在 63 K 时几乎比之前在约 200 K 时测量的值大两个数量级。我们还观察到甲氧基自由基产物的形成，该产物最近在太空中被检测到。这些结果通过形成氢键复合物来解释，该复合物的寿命足够长，可以进行量子力学隧穿以形成产物。我们假设，OH 对有机分子的这种隧穿氧化机制在低温星际环境中普遍存在。
