Ricca Alessandra, Bauschlicher Charles W, Roser Joseph E, Peeters Els
Carl Sagan Center, SETI Institute, 189 Bernardo Ave., Mountain View, CA 94043.
Space Science & Astrobiology Division, Astrophysics Branch, Mail Stop 245-6, NASA Ames Research Center, Moffett Field, CA 94035.
Astrophys J. 2018;854(No 2). doi: 10.3847/1538-4357/aaa757. Epub 2018 Feb 16.
We have investigated the mid-infrared spectral characteristics of a series of polycyclic aromatic hydrocarbons (PAHs) with straight edges and containing an even or odd number of carbons using density functional theory (DFT). For several even and odd-carbon PAHs, the 8.6/6.2 and 7.6/6.2 intensity ratios computed in emission after the absorption of a 8 eV photon match the observed ratios obtained for three reflection nebulae (RNe), namely NGC 1333, NGC 7023, and NGC 2023. Odd-carbon PAHs are favored, particularly for NGC 1333. Both cations and anions are present with the cations being predominant. Relevant PAHs span sizes ranging from 46 to 103-113 carbons for NGC 7023 and NGC 2023 and from 38 to 127 carbons for NGC 1333 and have symmetries ranging from D to C . Our work suggests that even and odd-carbon PAHs with straight edges are viable candidates for the PAH emission seen towards irradiated Photo-Dissociation Regions (PDRs).
我们使用密度泛函理论（DFT）研究了一系列具有直边且含偶数或奇数个碳原子的多环芳烃（PAH）的中红外光谱特征。对于几种偶数和奇数碳的PAH，在吸收8 eV光子后发射中计算出的8.6/6.2和7.6/6.2强度比与在三个反射星云（RNe），即NGC 1333、NGC 7023和NGC 2023中观测到的比值相匹配。奇数碳的PAH更受青睐，特别是对于NGC 1333。阳离子和阴离子都存在，且阳离子占主导。对于NGC 7023和NGC 2023，相关PAH的大小范围为46至103 - 113个碳，对于NGC 1333，范围为38至127个碳，其对称性范围从D到C 。我们的工作表明，具有直边的偶数和奇数碳PAH是朝向受辐照光解离区（PDR）观测到的PAH发射的可行候选物。
