苯乙炔及其氘代同位素在中远红外区域的吸收光谱
The Infrared Absorption Spectrum of Phenylacetylene and its Deuterated Isotopologue in the Mid- to Far-IR
AI总结：
本研究通过实验与计算结合，揭示苯乙炔及其氘代同位素在中远红外光谱中的非谐性效应，表明包含多量子模式的非谐性处理对解析PAH红外光谱至关重要。
摘要：
非谐性强烈影响多环芳烃（PAH）分子的吸收和发射光谱。本文通过红外-紫外离子偶联光谱实验，结合详细的非谐性计算，揭示了苯乙炔及其单氘代同位素在中远红外吸收光谱中基频、泛频以及双量子和三量子组合带跃迁的存在。在400-900 cm$^{\rm -1}$范围内的强吸收特征源于CH(D)面内和面外摇摆及弯曲振动，以及包括乙炔取代基的C$\equiv$C键和CH键及芳香环在内的弯曲运动。对于苯乙炔，每个吸收特征都直接或间接地归属于单个或多个振动模式。实测光谱在许多区域密集、宽泛且无结构，但通过计算得到了很好的表征。氘代后，观察到较大的同位素位移。对于d$_1$-苯乙炔，在1500 cm$^{\rm -1}$以上的频率，计算与实验呈现一一对应关系，所有特征均归属于组合带和泛频。苯乙炔中观察到的C$\equiv$C伸缩振动在d$_1$-苯乙炔中未观察到，这是由于计算得到的强度下降了40倍。总体而言，包含双量子和三量子模式的仔细非谐性处理对于理解苯乙炔红外光谱的丰富细节至关重要。基于这些结果，可以预期这种全面包容的非谐性处理也将是解析一般PAH红外光谱的关键。
英文摘要：
Anharmonicity strongly influences the absorption and emission spectra of polycyclic aromatic hydrocarbon (PAH) molecules. Here, IR-UV ion-dip spectroscopy experiments together with detailed anharmonic computations reveal the presence of fundamental, overtone, as well as 2- and 3-quanta combination band transitions in the far- and mid-infrared absorption spectrum of phenylacetylene and its singly deuterated isotopologue. Strong absorption features in the 400-900 cm$^{\rm -1}$ range originate from CH(D) in-plane and out-of-plane wags and bends, as well as bending motions including the C$\equiv$C and CH bonds of the acetylene substituent and the aromatic ring. For phenylacetylene, every absorption feature is assigned either directly or indirectly to a single or multiple vibrational mode(s). The measured spectrum is dense, broad, and structureless in many regions but well characterized by computations. Upon deuteration, large isotopic shifts are observed. At frequencies above 1500 cm$^{\rm -1}$ for d$_1$-phenylacetylene, a one-to-one match is seen when comparing computations and experiment with all features assigned to combination bands and overtones. The C$\equiv$C stretch observed in phenylacetylene is not observed in d$_1$-phenylacetylene due to a computed 40-fold drop in intensity. Overall, a careful treatment of anharmonicity that includes 2- and 3-quanta modes is found to be crucial to understand the rich details of the infrared spectrum of phenylacetylene. Based on these results, it can be expected that such an all-inclusive anharmonic treatment will also be key for unraveling the infrared spectra of PAHs in general.
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