物理化学学报 >> 2003, Vol. 19 >> Issue (07): 661-665.doi: 10.3866/PKU.WHXB20030720

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甲烷在飞秒强激光场中的解离

唐晓萍;王素凡;高丽蓉;王操;孔繁敖   

  1. 中国科学院化学研究所, 分子反应动力学实验室,北京　100080
  • 收稿日期:2002-10-08 修回日期:2003-03-03 发布日期:2003-07-15
  • 通讯作者: 孔繁敖 E-mail:kong@mrdlab.icas.ac.cn

Dissociation of Methane in Intense Femtosecond Laser Field

Tang Xiao-Ping;Wang Su-Fan;Gao Li-Rong;Wang Cao;Kong Fan-Ao   

  1. Institute of Chemistry, Chinese Academy of Sciences, Beijing　100080
  • Received:2002-10-08 Revised:2003-03-03 Published:2003-07-15
  • Contact: Kong Fan-Ao E-mail:kong@mrdlab.icas.ac.cn

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摘要： 用波长为800 nm，脉宽为160 fs，强度范围为7.6×1013～1.4×1014 W•cm－2的强激光使甲烷分子解离，并用质谱仪检测产生的离子.母体离子在较低的激光强度（7.6×1013 W•cm－2）下出现;当激光强度增加到8.0×1013 W•cm－2时，开始出现；CH2＋、CH＋和C＋离子出现的阈值分别为1.0×1014 W•cm－2、1.4×1014 W•cm－2和1.4×1014 W•cm－2.这些现象表明甲烷的解离是一个顺序过程.质谱图中没有多电荷离子，因此排除了发生库仑爆炸的可能.以线偏振激光作用于甲烷，只有H＋离子有各向异性的角度分布，暗示分子中的化学键是被激光外场拉断的，且初级产物离子H＋是沿着激光电场的方向飞出.提出的准双原子分子模型较好地解释了实验结果.

关键词: 飞秒激光, 强激光场, 甲烷, 飞行时间质谱, 解离

Abstract: Methane molecules were irradiated by a laser beam in the intensity range of 7.6 ×1013～1.4×1014 W•cm－2 (800 nm, 160 fs). A time of flight mass spectrometer was coupled to the laser system. The parent ions can be seen at low laser intensity of 7.6×1013 W•cm－2. When the laser intensity increases to 8 .0×1013 W•cm－2, CH3＋ ions appear. The appearance of the CH2＋, CH＋, C＋ ions are at the laser intensities of 1.0×1014 W•cm－2, 1.4×1014 W•cm－2 and 1.4×1014 W•cm－2, respectively. The facts show that dissociation of methane is a step-wise process. Coulomb explosion does not happen during the dissociation because no multi-electron ions are found in the mass spectra. Only H＋ ion yield has anisotropic angular distribution when methane is irradiated by a linearly polarized laser. This fact implies that the chemical bonds in the molecule are pulled off by the laser field and that the H＋ ion flies along the direction of the laser electronic field. The quasi-diatomic molecule model we proposed can explain the experimental results satisfactorily.

Key words: Femtosecond laser, Intense laser field, Methane, TOFMS, Dissociation