非常大的、紧凑的、高度对称的多环芳烃（PAHs）的红外光谱
The infrared spectra of very large, compact, highly symmetric, polycyclic aromatic hydrocarbons (PAHs)
摘要：
用密度泛函理论计算了C54 H18 ~ C130 H28大分子多环芳烃的中红外光谱。作为PAH的大小，电荷和几何形状的函数的频带的位置和强度的趋势进行了讨论。关于3.3、6.3和11.2微米波段，与小多环芳烃的结论相似。这并不适用于其他功能。较大的PAH阳离子和阴离子在7.8微米处产生谱带，并且随着PAH尺寸的增加，8.5微米附近的谱带变得突出并略微向红色偏移。此外，平均阴离子峰略微下降至平均阳离子峰的红色。7.8和8.6微米波段的行为与天文观测的相似性表明，它们来自大的阳离子和阴离子多环芳烃，特定的峰位和轮廓反映了多环芳烃阳离子与阴离子的浓度比和多环芳烃大小的相对强度。因此，7.7微米宽的天文波段是由小的和大的多环芳烃阳离子和阴离子的混合物产生的，小的和大的多环芳烃分别对7.6和7.8微米的成分贡献更大。对于CH的面外振动，双氢与单独的振动耦合，并产生与较小的多环芳烃中的对应物波长略有不同的带。因此，先前推导的PAH结构被改变，有利于更紧凑和对称的形式。此外，双波段和三波段之间的重叠可能会重现蓝色阴影的12.8微米轮廓。
英文摘要：
The mid-infrared spectra of large PAHs ranging from C54H18 to C130H28 are determined computationally using Density Functional Theory. Trends in the band positions and intensities as a function of PAH size, charge and geometry are discussed. Regarding the 3.3, 6.3 and 11.2 micron bands similar conclusions hold as with small PAHs. This does not hold for the other features. The larger PAH cations and anions produce bands at 7.8 micron and, as PAH sizes increases, a band near 8.5 micron becomes prominent and shifts slightly to the red. In addition, the average anion peak falls slightly to the red of the average cation peak. The similarity in behavior of the 7.8 and 8.6 micron bands with the astronomical observations suggests that they arise from large, cationic and anionic PAHs, with the specific peak position and profile reflecting the PAH cation to anion concentration ratio and relative intensities of PAH size. Hence, the broad astronomical 7.7 micron band is produced by a mixture of small and large PAH cations and anions, with small and large PAHs contributing more to the 7.6 and 7.8 micron component respectively. For the CH out-of-plane vibrations, the duo hydrogens couple with the solo vibrations and produce bands that fall at wavelengths slightly different than their counterparts in smaller PAHs. As a consequence, previously deduced PAH structures are altered in favor of more compact and symmetric forms. In addition, the overlap between the duo and trio bands may reproduce the blue-shaded 12.8 micron profile.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
