Photoelectron imaging of resonance-enhanced multiphoton ionization and above-threshold ionization of ammonia molecules in a strong 800-nm laser pulse

Song Le-Le^{1, 2, 3}, Sun Ya-Nan^{1, 3}, Wang Yan-Hui⁴, Wang Xiao-Chun^{1, 3}, He Lan-Hai^{1, 3}, Luo Si-Zuo^{1, 3}, Hu Wen-Hui^{1, 3}, Tong Qiu-Nan^{1, 3}, Ding Da-Jun^{1, 3}, Liu Fu-Chun^{1, 3, †}

Energy shifts of NH₃ molecular Rydberg states by adding ponderomotive force potential energy into the total energy. Without ponderomotive force, ionization potential of ammonia is 10.18 eV, and values of A, B, C, D, E states are 5.73 eV, 7.34 eV, 7.92 eV, 8.65 eV, 9.04 eV, respectively. The 7.75 eV, 9.3 eV, and 10.85 eV horizontal lines are values for 5 photons, 6 photons, and 7 photons.