论文标题
光解离区域中的多环芳烃发射模型i：应用于3.3、6.2和11.2 $μ$ m频段
Polycyclic Aromatic Hydrocarbon emission model in photodissociation regions I: Application to the 3.3, 6.2, and 11.2 $μ$m bands
论文作者
论文摘要
我们提出了一个基于电荷分布的模型，该模型使用最新的测量值或特定PAH的量子化学计算来计算多环芳烃（PAH）分子的红外光谱。该模型应用于具有良好确定的物理条件（辐射场强度，$ g_ {0} $，电子密度$ n_ {e} $的样本（PDRS）样品（PDRS），$ g_ {0} $，$ n_ {e} $，$ t _ {\ rm as as as} $）。具体而言，我们建模了五个PAH的发射范围从18至96个碳原子，在以电离参数为特征的一系列物理条件下，以电离参数$γ= g_ {0} \ times t _ {\ rm Gas}^{1/2} {1/2}/n_ {e} $。阴离子以低$γ$（$ <2 \ times 10^{2} $）环境中的主要电荷载体出现，中间$γ$（$ 10^{3} - 10^{4} $）环境，以及高$umγ$（$> 10^{5} $）的阳离子。此外，PAH阴离子和阳离子具有相似的光谱特征。阳离子和阴离子光谱的相似性转化为对6.2/（11.0+11.2）带比的解释，该比率很高，与阳离子或阴离子的大贡献相关。该模型的预测值为6.2/（11.0+11.2）和3.3/6.2，与PDRS NGC 7023，NGC 2023，Morsehead星云，猎户座棒和差异ISM的观测值进行了很好的比较，表明电荷状态的变化可以解释观察到的PAH的变化。我们还重新评估6.2/（11.0+11.2）vs 3.3/（11.0+11.2）比率的诊断潜力，并表明，如果没有任何关于$γ$的任何先验知识，3.3/（11.0+11.2）可以预测PAH的大小，但是6.2/（11.0+11.2）无法预测$γ$的Arostoplopsical of Altoplopsical of Altoplopsical of Altoploplopsical of Altoplopsical of Altoplopsical of Altoplopsical of Altoploplopsical of Altoploplopsical of Altoploploploplopsical。
We present a charge distribution based model that computes the infrared spectrum of polycyclic aromatic hydrocarbon (PAH) molecules using recent measurements or quantum chemical calculations of specific PAHs. The model is applied to a sample of well-studied photodissociation regions (PDRs) with well-determined physical conditions (the radiation field strength, $G_{0}$, electron density $n_{e}$, and the gas temperature, $T_{\rm gas}$). Specifically, we modelled the emission of five PAHs ranging in size from 18 to 96 carbon atoms, over a range of physical conditions characterized by the ionization parameter $γ= G_{0}\times T_{\rm gas}^{1/2}/n_{e}$. The anions emerge as the dominant charge carriers in low $γ$ ($< 2\times 10^{2}$) environments, neutrals in the intermediate $γ$ ($10^{3} - 10^{4}$) environments, and cations in the high $γ$ ($ > 10^{5}$) environments. Furthermore, the PAH anions and cations exhibit similar spectral characteristics. The similarity in the cationic and anionic spectra translates into the interpretation of the 6.2/(11.0+11.2) band ratio, with high values of this ratio associated with large contributions from either cations or anions. The model's predicted values of 6.2/(11.0+11.2) and 3.3/6.2 compared well to the observations in the PDRs NGC 7023, NGC 2023, the horsehead nebula, the Orion bar, and the diffuse ISM, demonstrating that changes in the charge state can account for the variations in the observed PAH emission. We also reassess the diagnostic potential of the 6.2/(11.0+11.2) vs 3.3/(11.0+11.2) ratios and show that without any prior knowledge about $γ$, the 3.3/(11.0+11.2) can predict the PAH size, but the 6.2/(11.0+11.2) cannot predict the $γ$ of the astrophysical environment.
