甲烷在飞秒强激光场中的解离  

Dissociation of Methane in Intense Femtosecond Laser Field

作　　者：唐晓萍[1] 王素凡[1] 高丽蓉[1] 王操[1] 孔繁敖[1] 

机构地区：[1]中国科学院化学研究所分子反应动力学实验室,北京100080

出　　处：《物理化学学报》2003年第7期661-665,共5页Acta Physico-Chimica Sinica

基　　金：国家自然科学基金(29973052);国家重点基础研究发展规划项目~~

摘　　要：用波长为800nm,脉宽为160fs,强度范围为7.6×1013～1.4×1014W·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(7.6×1013W·cm-2)下出现;当激光强度增加到8.0×1013W·cm-2时,CH3+开始出现;CH2+、CH+和C+离子出现的阈值分别为1.0×1014W·cm-2,1.4×1014W·cm-2和1.4×1014W·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.Methane molecules were irradiated by a laser beam in the intensity range of 7.6 x 10(13) similar to 1.4 x 10(14) 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 x 10(13) W.cm(-2). When the laser intensity increases to 8.0 x 10(13) W.cm(-2), CH3+ ions appear. The appearance of the CH2+, CH+, C+ ions are at the laser intensities of 1.0 X 10(14) W.cm(-2), 1.4 x 10(14) W.cm(-2) and 1.4 X 10(14) 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.

关 键 词：甲烷 飞秒强激光场 解离 飞行时间质谱 

分 类 号：O644.18[理学—物理化学]