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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >H elimination and metastable lifetimes in the UV photoexcitation of diacetylene
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H elimination and metastable lifetimes in the UV photoexcitation of diacetylene

机译：二乙炔的紫外光激发中的H消除和亚稳寿命

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摘要

We present an experimental investigation of the UV photochemistry of diacetylene under collisionless conditions. The H loss channel is studied using DC slice ion imaging with two-color reduced-Doppler detection at 243 nm and 212 nm. The photochemistry is further studied deep in the vacuum UV, that is, at Lyman-alpha(121.6 nm).Translational energy distributions for the H + C_4H product arising from dissociation of C_4H_2 after excitation at 243, 212, and 121.6 nm show an isotropic angular distribution and characteristic translational energy profile suggesting statistical dissociation from the ground state or possibly from a low-lying triplet state. From these distributions, a two-photon dissociation process is inferred at 243 nm and 212 nm, whereas at 121.6 nm, a one-photon dissociation process prevails. The results are interpreted with the aid of ab initio calculations on the reaction pathways and statistical calculations of the dissociation rates and product branching. In a second series of experiments, nanosecond time-resolved phototionization measurements yield a direct determination of the lifetime of metastable triplet diacetylene under collisionless conditions, as well as its dependence on excitation energy. The observed submicrosecond lifetimes suggest that reactions of metastable diacetylene are likely to be less important in Titan's atmosphere than previously believed.
机译：我们提出了在无碰撞条件下联乙炔的紫外光化学实验研究。使用DC切片离子成像技术在243 nm和212 nm处进行双色还原多普勒检测，研究了H损失通道。在真空紫外线的更深处即莱曼-阿尔法（121.6 nm）处对光化学进行了进一步研究。在243、212和121.6 nm激发后，由于C_4H_2离解而引起的H + C_4H产物的平移能量分布显示出各向同性角分布和特征性平移能谱暗示了与基态或可能与低洼三重态的统计解离。根据这些分布，可以推断出在243 nm和212 nm处的双光子解离过程，而在121.6 nm处则以单光子解离过程为主。借助从头算起反应路径的计算以及解离速率和产物分支的统计计算来解释结果。在第二系列实验中，纳秒级时间分辨的光化反应测量结果可直接确定亚稳态三重态联乙炔在无碰撞条件下的寿命及其对激发能的依赖性。观察到的亚微秒寿命表明，亚坦二乙炔的反应在泰坦大气中的重要性可能不如先前认为的重要。

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