在离子速度成像的实验装置中, 将波长为492～523 nm范围内的激光倍频, 以经过倍频的激光作光源, 将碘甲烷分子(CH3I)电离, 获得了碘甲烷母体分子离子(CH3I+)在76 500～81 120 cm^-1范围内的高分辨双光子电离光谱; 介绍了CH3I的双光子电离机制, 根据Rydberg公式和量子数亏损成功对实验所得到的CH3I+谱中的46个谱峰做了标识, 并观察到了CH3I+谱中p, d, f系列的能级分裂. 标识结果表明, 在CH3I的双光子电离谱中除了可以观察到单光子电离谱的特征, 还可以观察到在单光子电离中禁阻的f系列跃迁.

Using the device for ion velocity imaging, the laser frequency is doubling with the wavelength in the region of 492-523 nm, and the laser after frequency doubling was used as the light source. The ion spectrum of methyl iodide parent molecular (CH3I+) in the range of 76 500-81 120 cm^-1 was obtained by the way of two-photon ionization, with a very high-resolution. The mechanisms of the methyl iodide molecule two-photon ionization were also described, the CH3I+ spectrum obtained in the experiment was marked based on Rydberg formula and the quantum defect, the split arising from p series, d series and f series levels was also explained, and the spectral assignment showed that the two-photon ionization of methyl iodide molecule can not only be used to observe the reported characteristics of single photon ionization, but also can find some transitions which is forbidden in the single photon ionization, such as f series transitions.