Investigation On Photoelectron Angular Distributions Of Molecules By EVV Fields

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.