恒星形成区的复杂化学：一个扩展的气体-颗粒升温化学模型
Complex Chemistry in Star-Forming Regions: An Expanded Gas-Grain Warm-up Chemical Model
摘要：
长期以来，气相过程被认为是恒星形成区域复杂有机分子的关键形成机制。然而，最近的实验和理论证据对这些过程的效率提出了质疑。颗粒表面化学经常被引用作为一种解决方案，但到目前为止，还没有考虑到恒星形成区域的高度化学复杂性和不断变化的物理条件的定量模型。在这里，我们介绍了一种新的气体颗粒化学网络，其中广泛的复杂物种可能会形成涉及自由基的反应。我们考虑的自由基（H，OH，CO，HCO，CH 3，CH 3 O，CH 2 OH，NH和NH 2）主要是由宇宙射线诱导的颗粒冰的光解离产生的，在较冷的早期演化阶段形成的。热核的逐渐升温对复杂分子的形成至关重要，这使得结合力更强的自由基能够在晶粒表面上移动。这种类型的化学能够再现Sgr B2（N）中所见的高度复杂性，并可以解释观察到的各种先前检测到的复杂有机分子（包括结构异构体）的丰度和温度。许多其他复杂的物种被这个模型预测，这些物种中的几个可能是在热的核心检测。高质量和低质量恒星形成的化学差异也得到了解决;更大的化学复杂性，预计在进化的时间尺度更长。
英文摘要：
Gas-phase processes were long thought to be the key formation mechanisms for complex organic molecules in star-forming regions. However, recent experimental and theoretical evidence has cast doubt on the efficiency of such processes. Grain-surface chemistry is frequently invoked as a solution, but until now there have been no quantitative models taking into account both the high degree of chemical complexity and the evolving physical conditions of star-forming regions. Here, we introduce a new gas-grain chemical network, wherein a wide array of complex species may be formed by reactions involving radicals. The radicals we consider (H, OH, CO, HCO, CH3, CH3O, CH2OH, NH and NH2) are produced primarily by cosmic ray-induced photodissociation of the granular ices formed during the colder, earlier stages of evolution. The gradual warm-up of the hot core is crucial to the formation of complex molecules, allowing the more strongly-bound radicals to become mobile on grain surfaces. This type of chemistry is capable of reproducing the high degree of complexity seen in Sgr B2(N), and can explain the observed abundances and temperatures of a variety of previously detected complex organic molecules, including structural isomers. Many other complex species are predicted by this model, and several of these species may be detectable in hot cores. Differences in the chemistry of high- and low-mass star-formation are also addressed; greater chemical complexity is expected where evolution timescales are longer.
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