C60 AS A PROBE FOR ASTROPHYSICAL ENVIRONMENTS

C60 AS A PROBE FOR ASTROPHYSICAL ENVIRONMENTS
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C60 作为天体物理环境的探测器

DOI：
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发表时间：
2016
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影响因子：
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通讯作者：
T. Henning
T. Henning
中科院分区：
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作者：
A. Brieva;R. Gredel;C. Jäger;F. Huisken;T. Henning

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C60分子最近通过其在18.9、17.4、8.5和7.0μm附近的四个活跃的分子内振动模式(T1u)在广泛的天体物理环境中被探测到。中红外发射带的强度已被用于推断富富勒烯区域的天体物理条件。实验室和理论文献中报道了这四个谱带的相对内禀强度(RIS)值差异很大，这阻碍了C60在天体物理源中的激发机制的推导。用我们的方法产生的C60样品的光谱分析提供了高度重复性的RI值，分别为100，25±1，26±1和40±4。将推断的C60发射带强度与天体物理数据进行比较表明，观察到的强度不能仅用荧光或热发射来解释。观测到的17.4μm/18.9μm发射比的大范围表明，要么发射带包含来自C60以外的发射体的显著贡献，要么C60振动模之间的布居分布受到热或紫外激发以外的物理过程的影响，例如来自新生C60的化学发光，或者可能是内能逆转换引起的庞加莱荧光。我们仔细分析了C60的中红外光谱中的弱活动基模和二阶模的影响，提出中性C60是在富富勒烯环境中观察到的6.49μm的未知发射带的载体。
The C60 molecule has been recently detected in a wide range of astrophysical environments through its four active intramolecular vibrational modes (T1u) near 18.9, 17.4, 8.5, and 7.0 μm. The strengths of the mid-infrared emission bands have been used to infer astrophysical conditions in the fullerene-rich regions. Widely varying values of the relative intrinsic strengths (RIS) of these four bands are reported in laboratory and theoretical papers, which impedes the derivation of the excitation mechanism of C60 in the astrophysical sources. The spectroscopic analysis of the C60 samples produced with our method delivers highly reproducible RIS values of 100, 25 ± 1, 26 ± 1 and 40 ± 4. A comparison of the inferred C60 emission band strengths with the astrophysical data shows that the observed strengths cannot be explained in terms of fluorescent or thermal emission alone. The large range in the observed 17.4 μm/18.9 μm emission ratios indicates that either the emission bands contain significant contributions from emitters other than C60, or that the population distribution among the C60 vibrational modes is affected by physical processes other than thermal or UV excitation, such as chemo-luminescence from nascent C60 or possibly Poincaré fluorescence resulting from an inverse internal energy conversion. We have carefully analyzed the effect of the weakly active fundamental modes and second order modes in the mid-infrared spectrum of C60, and propose that neutral C60 is the carrier of the unidentified emission band at 6.49 μm which has been observed in fullerene-rich environments.