飞秒激光场中甲醇产物离子的角分布

利用直流切片离子成像技术结合飞行时间质谱技术,我们研究了甲醇(CH_3OH)分子在800 nm飞秒激光场中的多光子解离和库仑爆炸过程.获得了甲醇分子在光场中的飞行时间质谱和产物离子的切片影像,分析得到了不同库仑爆炸通道碎片离子的动能分布和角度分布.本文对比分析了C-O键断裂产生H_2O~+的H转移通道和产生OH~+的非H转移通道的角分布,计算了不同激光强度下两个通道的各向异性参数α_2和(cos~2θ),并根据产物离子角度分布与激光强度和离子价态的关系,揭示了甲醇分子在飞秒光场中的准直机制为动力学准直.

Angular distributions of photo-fragment ions of CH3OH molecules in the femtosecond laser fields

The multi-photon dissociation and coulomb explosion of methanol in the femtosecond laser field have been investigated by dc-slice imaging technique combined with time of flight mass spectroscopy. Time of flight mass spectroscopy and sliced images of fragment ions were obtained, and the kinetic energy release and angular distributions of photo-fragment ions were also measured. The kinetic energy release of CH₂⁺,H₂O⁺ and CH₃⁺,OH⁺ meet the conservation of momentum, it is proved that they come from process of Coulomb explosion. Based on the comparison of the migration pathway and non-migration pathway from the C-O bond cleavage, the intensity dependence of the anisotropy parameter a₂ and cos²θ values for each channel were calculated, which indicated the dynamic molecular alignments of methanol in the femtosecond laser fields dominates.