Wu Zhifeng, Wu Chengyin, Liang Qingqing, Wang Sufan, Liu Min, Deng Yongkai, Gong Qihuang
State Key Laboratory for Mesoscopic Physics, Department of Physics, Peking University, Beijing 100871, People's Republic of China.
J Chem Phys. 2007 Feb 21;126(7):074311. doi: 10.1063/1.2472341.
The fragmentation pattern of CH4 was experimentally studied at an intensity of approximately 10(14) W/cm2 with laser durations varying from 8 to 110 fs. When the laser duration was 8 fs, only the primarily fragmental CH3+ ion was observed in addition to the parent CH4+ ion. When the laser duration was 30 fs, small fragmental CH2+ and H+ ions appeared. When the laser duration was 110 fs, some doubly charged ions were also observed in addition to the abundant singly charged ions. The large mass spectra difference demonstrated that the pulse duration had a strong effect on the fragmentation of the parent ion produced in the single ionization. The effect of laser intensity on the fragmentation of CH4+ was also studied for few-cycle femtosecond laser pulses. The results demonstrated that the first-return recollision between the rescattered electron and the parent ion played a significant role in the fragmentation dynamics of the parent ion. Depending on the ion-electron impact energy, the recollision excited the parent ion to a dissociated state or doubly charged state. The experimentally observed singly charged fragmental ions resulted from the recollision-induced dissociation of CH4+ or the Coulomb explosion of CH(4)2+.
在激光强度约为10(14)W/cm2、激光持续时间从8飞秒到110飞秒变化的条件下，对CH4的碎裂模式进行了实验研究。当激光持续时间为8飞秒时，除了母体CH4+离子外，仅观察到主要的碎裂产物CH3+离子。当激光持续时间为30飞秒时，出现了小的碎裂产物CH2+和H+离子。当激光持续时间为110飞秒时，除了大量的单电荷离子外，还观察到了一些双电荷离子。质谱的巨大差异表明，脉冲持续时间对单电离产生的母体离子的碎裂有强烈影响。还研究了少周期飞秒激光脉冲的激光强度对CH4+碎裂的影响。结果表明，再散射电子与母体离子之间的首次返回重碰撞在母体离子的碎裂动力学中起重要作用。根据离子-电子碰撞能量，重碰撞将母体离子激发到解离态或双电荷态。实验观察到的单电荷碎裂离子是由CH4+的重碰撞诱导解离或CH(4)2+的库仑爆炸产生的。
