Fullerenes are the largest molecules identified so far in the interstellar medium. The spectroscopic properties of C₆₀ and its charge variants have been extensively studied in the mid-infrared, near-ultraviolet, and visible regions. On the other hand, the near-infrared (NIR) spectral region has remained relatively unexplored, in particular for neutral C₆₀. Here, we report the first measurements of the absorption spectra of solid C₆₀ from 6052 to 3596 cm^–1 (from 1.65 to 2.78 μm) recorded over the 11–300 K temperature range. The NIR spectra of C₆₀ microcrystals embedded in solid KBr were measured using a low-temperature helium cryo-cooling setup coupled to a Fourier transform infrared spectrometer. The observed spectra of C₆₀ from 1.65 to 2.78 μm show highly structured absorption features. Compared to isolated molecules, the lower symmetry of C₆₀ microcrystals optically activates many fundamental vibrational modes, which combine (up to 4-quanta) and contribute to the rich observed spectrum. Quantum chemical calculations and group theoretical analysis were performed for a tentative assignment of the observed combination and overtone bands to the calculated transitions of both regions by identifying the IR-active T_1u symmetries. A total of 3895 combination and overtone transitions were calculated in the region between 1.65 and 2.78 μm, amongst which 1862 transitions belong to the IR-active T_1u symmetry, expected to be observed in the absorption spectrum of gas-phase C₆₀. This work offers some guidance for future low-temperature gas-phase NIR absorption spectroscopic studies of C₆₀. Measurements of vibrational overtone bands of C₆₀ are extremely timely for the identification of the carriers of NIR DIBs (diffuse interstellar bands) in the context of the upcoming launch of the James Webb Space Telescope.

中文翻译：

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固相富勒烯C ₆₀在1.65和2.78μm之间的吸收光谱

富勒烯是迄今为止在星际介质中鉴定出的最大分子。C ₆₀及其电荷变体的光谱性质已在中红外，近紫外和可见光区域进行了广泛研究。另一方面，近红外（NIR）光谱区域仍然相对未开发，特别是对于中性C _60而言。在这里，我们报告了在11–300 K温度范围内记录的对固体C ₆₀从6052到3596 cm ^-1（从1.65到2.78μm）的吸收光谱的首次测量。C ₆₀的近红外光谱使用与傅立叶变换红外光谱仪耦合的低温氦冷冻冷却装置测量了嵌入KBr中的微晶。观察到的C ₆₀从1.65到2.78μm的光谱显示出高度结构化的吸收特征。与分离的分子相比，C ₆₀微晶的较低对称性光学激活了许多基本的振动模式，这些振动模式组合在一起（最多4个量子点）并有助于形成丰富的观察光谱。进行了量子化学计算和组理论分析，以便通过识别红外活性T _{1 u}将观察到的组合和泛音谱带暂定为两个区域的计算跃迁。对称性。在1.65和2.78μm之间的区域中总共计算出3895个组合和泛音跃迁，其中1862个跃迁属于IR活性T _{1 u}对称性，有望在气相C ₆₀的吸收光谱中观察到。这项工作为将来对C ₆₀的低温气相NIR吸收光谱研究提供了一些指导。在詹姆斯·韦伯太空望远镜即将发射时，对C ₆₀的振动泛音带进行测量非常及时，以识别NIR DIB（弥散星际带）的载波。