发表机构
NASA Ames Research Center; SETI Institute; Space Telescope Science Institute; University of North Carolina, Chapel Hill; The University of Western Ontario; Cardiff University; California Institute of Technology; ACRI-ST; Centre d’Etudes et de Recherche de Grasse (CERGA)（美国宇航局艾姆斯研究中心; SETI研究所; 太空望远镜科学研究所; 北卡罗来纳大学教堂山分校; 韦仕敦大学（西安大略大学）; 卡迪夫大学; 加州理工学院; ACRI-ST; 格拉斯研究与研究中心）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过从头算分子动力学和密度泛函理论建模氢化碳质颗粒，发现其发射光谱与JWST观测的D类源相符，提出其碎裂演化形成多环芳烃和富勒烯的假设。
AI 中文摘要
许多富碳后渐近巨分支星的红外光谱以芳香族和脂肪族烃的发射特征为主，但载体的化学结构仍未被识别。D类源显示出不寻常的发射轮廓，具有强烈的脂肪族发射，为候选载体提供了严格的检验。在此，我们研究氢化碳质分子颗粒是否可能是这些特征的载体。我们并非假设候选几何结构，而是利用从头算分子动力学模拟生成初始结构，并使用密度泛函理论对其进行优化。然后，我们将计算得到的发射光谱与JWST NIRSpec和MIRI/MRS对D类源的观测结果进行比较。提供最佳一致性的结构包含相当大的区域，这些区域具有带缺陷的芳香族和氢化芳香族，通过脂肪族桥连接，这与由脂肪族和烯烃桥连接的孤立二至三环芳香族的“arophatic”簇模型形成对比。作为一个代表性示例，我们详细讨论了分子颗粒C130H96（半径为5.5 Å），并将其计算光谱与IRAS 05110-6616（一个D2类源，具有芳香族C-H面外波段的明显位移）的JWST光谱进行比较。计算光谱与观测到的3微米轮廓、脂肪族C-H弯曲波段、8微米宽特征、11-14微米C-H面外区域以及16和21微米处的波段定性一致。我们假设，紫外光驱动这些分子颗粒的碎裂会释放出由脂肪族连接的芳香族，随后随着这些天体演化为行星状星云，形成多环芳烃和富勒烯。
英文摘要
The infrared spectra of many carbon-rich post-asymptotic giant branch stars are dominated by emission features from aromatic and aliphatic hydrocarbons, but the chemical structure of the carriers remains unidentified. Class D sources show unusual emission profiles with strong aliphatic emission, providing a stringent test of carrier candidates. Here we investigate whether hydrogenated carbonaceous molecular particles can be the carriers of these features. Rather than assuming candidate geometries we generate the initial structures using ab initio molecular dynamics simulations and optimize them using density functional theory. We then compare the computed emission spectra to JWST NIRSpec and MIRI/MRS observations of Class D sources. The structures providing the best agreements contain sizeable domains with defect-bearing aromatics and hydrogenated-aromatics connected by aliphatic bridges, in contrast to the "arophatic" cluster model of isolated two- to three-ring aromatics connected by aliphatic and olefinic bridges. As a representative example, we discuss in detail the molecular particle C130H96 (radius of 5.5 A) and compare its computed spectrum to the JWST spectra of IRAS 05110-6616, a Class D2 source with apparent shifts of the aromatic C-H out-of-plane bands. The calculated spectra are in qualitative agreement with the observed 3 micron profile, the aliphatic C-H bending bands, the broad 8 micron feature, the 11-14 micron C-H out-of-plane region, and the bands at 16 and 21 microns. We hypothesize that UV photo-driven fragmentation of such molecular particles releases aromatics linked by aliphatics, followed by the formation of polycyclic aromatic hydrocarbons and fullerenes as these objects evolve into planetary nebulae.
