The interaction of atoms and molecules with intense laser field occur manynonlinear behaviors, such as multiphoton ionization (MPI), above-threshold ionization(ATI), field ionization, field-assisted dissociation (FAD) and Coulomb explosion. Inthis paper we use30fs FEL to investigate on photoelectron angular distributions of O2and C2H2by velocity map imaging method. Oxygen molecule is ionized singly byone-photon process by ultrafast (30fs) extreme-ultraviolet (51nm) free-electron laserpulses with one photon energy of23.4eV. Based on photoelectron energy spectra, weanalyze electrons are ionized from X2∏g、a4∏u、b4∑g-、B2∑g-、and32∏uelectron states,respectively. And the fragments of O+and O2+by coulomb explosion are found. Theelectrons from C2H2ionized be judged from2∏gand2∑g+states by using54nm (23eV)FEL. |