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Photofragment Imaging of HNCO Decomposition at 210 nm: the Primary NH(a1¢)+CO(X1§+) Channel
Hua Wang,Shi-lin Liu*,Jie Liu,Feng-yan Wang,Bo Jiang,Xue-ming Yang*
Author NameAffiliationE-mail
Hua Wang Hefei National Laboratory for Physical Sciences at Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China  
Shi-lin Liu* Hefei National Laboratory for Physical Sciences at Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China slliu@ustc.edu.cn 
Jie Liu State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Science, Dalian 116023, China  
Feng-yan Wang State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Science, Dalian 116023, China  
Bo Jiang State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Science, Dalian 116023, China  
Xue-ming Yang* State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Science, Dalian 116023, China xmyang@dicp.ac.cn 
Abstract:
The photodissociation of isocyanic acid (HNCO) on the ˉrst excited singlet state following the excitation at 210 nm was investigated with an ion velocity slice imaging technique by probing the CO fragment. It was found from the (2+1) resonance-enhanced multi-photon ionization (REMPI) spectrum that the CO fragments are rotationally hot with population up to Jmax=50. The velocity imagings of the CO fragments at JCO=30 and 35 indicate that formation of NH(a1¢)+CO(X1§+, v=0) is the predominant dissociation channel at 210 nm. From analysis of the CO fragment translational energy distributions, the NH(a1¢) fragment was observed to be rotationally cold, about half of the available energy was partitioned into the translational motion of fragments after dissociation, and the NH(a1¢)+CO(X1§+) dissociation threshold was determined at 42738§30 cm?1. From analysis of the CO fragment angular distributions, the dissociation anisotropy parameter ˉ was found to be negative, and increasing with the rotational quantum number of the NH fragment, i.e., from ?0.75 at JNH=2-4 to ?0.17 at JNH=11. Impulsive direct and vertical dissociation process of HNCO on the singlet state at 210 nm was conˉrmed experimentally. A classical impact dissociation model was employed to explain the dependence of the ˉ value on the rotational excitation of the NH fragment.
Key words:  Isocyanic acid, Dissociation dynamics, Velocity slice imaging, Dissociation energy, Fragment angular distribution, Translational energy distribution
FundProject:国家自然科学基金
离子速度成像法研究HNCO分子在210 nm的光解动力学
汪华,刘世林*,刘杰,王凤燕,姜波,杨学明*
摘要:
用三维离子速度成像方法研究了HNCO分子在210 nm光解下的光解动力学.得到了光解产物CO在不同转动态的角分布和平动能分布.结果表明,HNCO分子在210 nm光解的主要通道是产生NH(a1¢)+CO(X1§+)的通道;碎片CO具有很高的转动激发,而NH的转动激发很小,约50%可资用能转化为平动能,该通道解离能确定为42738 cm?1;解离各向异性参数ˉ 最小为?0.75,且随着NH转动激发增大.该研究首次实验上证实了HNCO分子的快速、直接解离过程.ˉ值随NH的转动变化可以用经典碰撞模型予以解释.
关键词:  HNCO,光解离,离子速度成像,解离能,平动能分布,角度分布
DOI:10.1088/1674-0068/20/04/388-394
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