摘要
The ionization processes of NH3 molecule are studied by photoelectron velocity map imaging technique in a linearly polarized 400-nm femtosecond laser field. The two-dimensional photoelectron images from ammonia molecules under different laser intensities are obtained. In the slow electron region, the values of kinetic energy of photoelectrons corresponding to peaks 1, 2, 3, and 4 are 0.27, 0.86, 1.16, and 1.6 eV, respectively. With both the kinetic energy and angular distribution of photoelectrons from NH3 molecules, we can confirm that the two-photon excited intermediate Rydberg state is A^1 A2" (v2'=3) state for photoelectron peaks 2, 3, 4, and the three peaks are marked as 1223 (2 + 2), 1123 (2 + 2), and 1023 (2 + 2) multi-photon processes, respectively. Then, peak 1 is found by adding a hexapole between the source chamber and the detection chamber to realize the rotational state selection and beam focusing. Peak 1 is labeled as the 1323 (3 + 1) multi-photon process through the intermediate Rydberg state E^1A1'. The phenomena of channel switching are found in the slow electron kinetic energy distributions. Our calculations and experimental results indicate that the stretching vibrational mode of ammonia molecules varies with channels, while the umbrella vibration does not. In addition, we consider and discuss the ac-Stark effect in a strong laser field. Peaks 5 and 6 are marked as (2 + 2 + 1) and (2 + 2 + 2) above threshold ionization processes in the fast electron region.
作者
Ya-Nan Sun
Yan-Hui Wang
Le-Le Song
Hai-Bin Du
Xiao-Chun Wang
Lan-Lai He
Si-Zuo Luo
Qin Yang
Jing Leng
Fu-Chun Liu
孙亚楠;王艳辉;宋乐乐;杜海滨;王晓春;赫兰海;罗嗣佐;杨钦;冷静;刘福春(Institute of Atomic and Molecular Physics,Jilin University,Changchun 130012,China;College of Electronic Science and Engineering,State Key Laboratory on Integrated Optoelectronics,Jilin University,Changchun 130012,China;Jilin Institute of Chemical Technology,Jilin 132022,China;Jilin Provincial Key Laboratory of Applied Atomic and Molecular Spectroscopy,Jilin University,Changchun 130012,China;Department of Comprehensive,Harbin City Vocational College,Haerbin 150000,China)
基金
Project supported by the National Natural Science Foundation of China (Grant Nos. 11574116, 11534004, and 10704028).
