The Investigation Of Photoelectron Imaging By Velocity Map Imaging Method

With the development of ultra-short and intense laser technology, the intensity of laser field is comparable with Coulomb potential, a lot of nonlinear behaviors of molecules under strong laser field become feasible in many laboratory, such as above-threshold ionization, field ionization and dissociation, Coulomb explosion.In this article, the interaction of oxygen, nitrogen, and carbon dioxide molecule with free-electron laser pulses(laser wavelength for51nm-62nm, pulse width30fs) was studied by velocity map imaging technique. The information of ionization process and dissociation channels be analyzed on the photoelectron imaging distributions.1From the spectrum of oxygen electron, we identify the five states of the O2. In the five states, X2Πg,a4Πu,32Πu is the bound state, b4Σg－, B4Σg－is the dissociation states. And we get the corresponding dissociation limit and dissociation channel. Dissociation limit is the18.73eV, the fragments of the dissociation produced O+ion and oxygen atoms. 2For nitrogen electron spectra, we identify the three states of the N2,in the three state X2Σg+,A2ΠU,B2ΣU+corresponding to bound states and there is no the dissociation states.3Analyzing of the electron spectra of carbon dioxide, we identify the three states of the CO2,X2Πg+,A2Πu+states is the bound state, C2Σg+is the dissociation state, C2Σg+had two predissociation channels, which produced O+,CO ions or CO+,O ions fragment.