物理化学学报 >> 2017, Vol. 33 >> Issue (10): 2004-2012.doi: 10.3866/PKU.WHXB201705183

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氧硫化碳在230nm光激发下的S(3P)解离通道

吴向坤,高治,于同坡,周晓国*(),刘世林   

  • 收稿日期:2017-04-22 发布日期:2017-07-17
  • 通讯作者: 周晓国 E-mail:xzhou@ustc.edu.cn
  • 基金资助:
    国家自然科学基金(21373194);国家自然科学基金(21573210);国家重点研发计划(2016YFF0200502);国家重点基础研究发展规划项目(973)(2013CB834602);国家重大科学仪器专项(2012YQ220113)

S(3P) Fragmentation Channel of Carbonyl Sulfide at 230 nm

Xiang-Kun WU,Zhi GAO,Tong-Po YU,Xiao-Guo ZHOU*(),Shi-Lin LIU   

  • Received:2017-04-22 Published:2017-07-17
  • Contact: Xiao-Guo ZHOU E-mail:xzhou@ustc.edu.cn
  • Supported by:
    the National Natural Science Foundation of China(21373194);the National Natural Science Foundation of China(21573210);National Key Research and Development Program(2016YFF0200502);National Key Basic Research Program of China (973)(2013CB834602);the Ministry of Science and Technology of China(2012YQ220113)

摘要:

在230 nm激光激发下,氧硫化碳(OCS)分子迅速解离生成振动基态但高转动激发的CO(X1Σg+v = 0,J = 42–69)碎片,并通过共振增强多光子电离技术实现其离子化。通过检测处于J = 56–69转动激发态CO碎片的离子速度聚焦影像,我们获得了各转动态CO碎片的速度分布和空间角度分布,其中包含了S(1D)+ CO的单重态和S(3PJ)+ CO三重态解离通道的贡献。不同的转动态CO碎片对应三重态产物通道的量子产率略有不同,经加权平均我们得到230 nm附近光解OCS分子中S(3P)解离通道的量子产率为4.16%。结合高精度量化计算的OCS分子势能面和吸收截面的信息,我们获得了OCS光解的三重态解离机理,即基态OCS(X1A')分子吸收一个光子激发到弯曲的A1A'态之后,通过内转换跃迁回弯曲构型的基电子态,随后在C―S键断裂过程中与23A"(c3A")态强烈耦合并沿后者势能面绝热解离。

关键词: 氧硫化碳, 光解离, 共振增强多光子电离, 通道分支比, 离子速度成像

Abstract:

Carbonyl sulfide (OCS) was photoexcited at 230 nm so that it dissociated into a vibrationally cold but rotationally hot CO (X1Σg+, v = 0, J = 42–69) fragment, which was eventually subjected to resonance enhanced multiphoton ionization. The kinetic energy release distribution and angular distribution of the CO fragment were obtained by detecting the time-sliced velocity map images of CO+ in various rotational states (J = 55–69), wherein both the singlet dissociation channel of S(1D) + CO and the triplet pathway of S(3PJ) + CO were involved. For the triplet fragment channel, the total quantum yield of OCS dissociation at 230 nm was estimated to be 4.16%, based on the measured branching ratioin every rotational state. High-level quantum chemical calculations on the potential energy surface and the absorption cross section of OCS revealed the dissociation mechanism along the triplet channel of OCS, with photolysis at 230 nm. The ground state OCS (X1A') is photoexcited to the bent A1A' state at 230 nm, which then decays back to X1A' in a bent structure via internal conversion and subsequently couples to the 23A"(c3A") state by spin-orbit coupling, followed by direct dissociation along its potential energy surface.

Key words: Carbonyl sulfide (OCS), Photodissociation, Resonance enhanced multiphoton ionization, Branching ratio, Ion velocity imaging

MSC2000: 

  • O643