THE HNC/HCN RATIO IN STAR-FORMING REGIONS
THE HNC/HCN RATIO IN STAR-FORMING REGIONS
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DOI：
10.1088/0004-637x/787/1/74
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发表时间：
2014-04
期刊：
影响因子：
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通讯作者：
D. Graninger;E. Herbst;K. Öberg;A. Vasyunin
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文献类型：
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作者：
D. Graninger;E. Herbst;K. Öberg;A. Vasyunin
HNC 和 HCN 通常用作分子云中的致密气体示踪剂，它们是一对异构体，由于具有温度依赖性、异构体特异性的形成和破坏途径，因此具有作为温度探针的巨大潜力。之前对 HNC/HCN 丰度比的观察表明，该比值随着温度的升高而降低，这是标准天体化学模型无法重现的。我们对环境特征和化学反应影响 HNC/HCN 比率的参数进行了详细的研究，从而有助于观察到的依赖性。使用更新了新反应和反应势垒的现有气体和气体颗粒模型，我们发现在静态模型中，H + HNC 气相反应在所有条件下调节 HNC/HCN 比率，除了非常早期的情况。我们定量限制了 H 丰度和 H + HNC 反应势垒的组合，这可以解释观察到的 HNC/HCN 温度依赖性，并根据新的量子化学计算讨论其含义。在预热模型中，气体颗粒化学对预测的 HNC/HCN 比率有显着贡献，因此了解恒星形成的动力学是模拟 HNC/HCN 系统的关键。
HNC and HCN, typically used as dense gas tracers in molecular clouds, are a pair of isomers that have great potential as a temperature probe because of temperature dependent, isomer-specific formation and destruction pathways. Previous observations of the HNC/HCN abundance ratio show that the ratio decreases with increasing temperature, something that standard astrochemical models cannot reproduce. We have undertaken a detailed parameter study on which environmental characteristics and chemical reactions affect the HNC/HCN ratio and can thus contribute to the observed dependence. Using existing gas and gas-grain models updated with new reactions and reaction barriers, we find that in static models the H + HNC gas-phase reaction regulates the HNC/HCN ratio under all conditions, except for very early times. We quantitatively constrain the combinations of H abundance and H + HNC reaction barrier that can explain the observed HNC/HCN temperature dependence and discuss the implications in light of new quantum chemical calculations. In warm-up models, gas-grain chemistry contributes significantly to the predicted HNC/HCN ratio and understanding the dynamics of star formation is therefore key to model the HNC/HCN system.