Tsuge Masashi, Tseng Chih-Yu, Lee Yuan-Pern
Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, 1001 Ta-Hsueh Road, Hsinchu 30010, Taiwan.
Phys Chem Chem Phys. 2018 Feb 21;20(8):5344-5358. doi: 10.1039/c7cp05680j.
para-Hydrogen (p-H) serves as a new host in matrix-isolation experiments for an investigation of species of astrochemical interest. Protonated and mono-hydrogenated species are produced upon electron bombardment during deposition of p-H containing a precursor in a small proportion. The applications of this novel technique to generate protonated polycyclic aromatic hydrocarbons (HPAH), protonated polycyclic nitrogen heterocycles (HPANH), and their neutral counterparts, which are important in the identification of interstellar unidentified infrared emission bands, demonstrate its superiority over other methods. The clean production with little fragmentation, ease of distinction between protonated and neutral species, narrow lines and reliable relative infrared intensities of the lines, and broad coverage of the spectral range associated with this method enable us to assign the isomers unambiguously. The application of this method to the protonation of small molecules is more complicated partly because of the feasible fragmentation and reactions, and partly because of the possible proton sharing between the species of interest and H, but, with isotopic experiments and secondary photolysis, definitive assignments are practicable. Furthermore, the true relative infrared intensities are critical to a comparison of experimental results with data from theoretical calculations. The spectra of a proton-shared species in solid p-H might provide insight into a search for spectra of proton-bound species in interstellar media. Investigations of hydrogenated species involving the photolysis of Cl or precursors of OH complement those using electron bombardment and provide an improved ratio of signal to noise. With careful grouping of observed lines after secondary photolysis and a comparison with theoretical predictions, various isomers of these species have been determined. This photolytic technique has been applied in an investigation of hydrogenated PAH and PANH, and the hydrogenation reactions of small molecules, which are important in interstellar ice and the evolution of life. The electronic transitions of molecules in solid p-H have been little investigated. The matrix shift of the origins of transitions and the spectral width seem to be much smaller than those of noble-gas matrices; these features might facilitate a direct comparison of matrix spectra with diffuse interstellar bands, but further data are required to assess this possibility. The advantages and disadvantages of applying these techniques of p-H matrix isolation to astrochemical research and their future perspectives are discussed.
仲氢（p-H）在基质隔离实验中作为一种新的主体，用于研究具有天体化学意义的物种。在沉积含有少量前体的p-H过程中进行电子轰击时，会产生质子化和单氢化物种。这项新技术用于生成质子化多环芳烃（HPAH）、质子化多环氮杂环（HPANH）及其中性对应物，这些对于识别星际未确认红外发射带很重要，展示了其相对于其他方法的优越性。该方法产生的碎片少、易于区分质子化和中性物种、谱线窄且谱线相对红外强度可靠，以及与该方法相关的光谱范围覆盖广泛，使我们能够明确地确定异构体。将该方法应用于小分子的质子化更为复杂，部分原因是存在可行的碎片化和反应，部分原因是感兴趣的物种与H之间可能存在质子共享，但是，通过同位素实验和二次光解，可以进行明确的归属。此外，真正的相对红外强度对于将实验结果与理论计算数据进行比较至关重要。固体p-H中质子共享物种的光谱可能有助于寻找星际介质中质子结合物种的光谱。涉及Cl或OH前体光解的氢化物种的研究补充了使用电子轰击的研究，并提供了更高的信噪比。通过对二次光解后观察到的谱线进行仔细分组并与理论预测进行比较，已经确定了这些物种的各种异构体。这种光解技术已应用于氢化PAH和PANH的研究以及小分子的氢化反应，这些在星际冰和生命演化中很重要。固体p-H中分子的电子跃迁研究较少。跃迁起源的基质位移和光谱宽度似乎比稀有气体基质的要小得多；这些特征可能有助于将基质光谱与漫射星际带进行直接比较，但需要更多数据来评估这种可能性。讨论了将这些p-H基质隔离技术应用于天体化学研究的优缺点及其未来前景。
