Autoionization And Coulomb Explosion Dynamic Of N₂O Molecules Under Femtosecond Laser Field

The study of ultrafast laser-matter interactions has given us the opportunity to understand dynamic processes such as ionization-dissociation of atoms and molecules on the femtosecond time scale and the angstrom spatial scale,and to further develop advanced techniques for their manipulations.Under the interaction of femtosecond laser fields,molecules are ionized and would induce the dissociation and Coulomb explosion.The corresponding ionization-dissociation dynamics can be analyzed in terms of both electrons and ions by coincidence measurement techniques.In this work,we have performed four-body coincidence measurements of the dissociative double ionization process of N2 O molecules under the action of an intense femtosecond laser using the cold target recoil momentum spectrometer(COLTRIMS)to study the autoionization and Coulomb explosion dynamic of N2 O molecules in a femtosecond laser field.A channel-resolved autoionization dynamics study was carried out.The results show that there is a dissociation path in the dissociation channel of N2 O molecules with a small kinetic energy release(KER).The dissociation path is presumed to originate from the dissociation of the autoionization N2O+* state,in comparison with the results of the existing studies on the autoionization state of N2 O molecules by extreme ultraviolet light.Gaussian deconvolution was used to fit the z-directional momentum of the ion and the pz,sum bimodal structure to obtain the asymmetry and the momentum of the two electrons exiting along both ends of the molecular axis.The momentum of one of the electrons along the z-direction is close to 0 a.u.In addition,the high-energy electrons in the autoionization dissociation path are identified as possibly originating from the HOMO-1 orbital based on the fitted results.In further momentum analysis of electrons,the ionization order of two electrons is distinguished according to the analysis of the electron momentum.The existence of low-energy electrons with kinetic energy peaks of only 1-2 e V,extending up to 20 e V,was observed in the experiments,in contrast to the slow electrons produced by single-photon induced autoionization with discrete fine peak structures and kinetic energies less than 2 e V,suggesting a modulating effect of the strong laser field on the autoionized electrons.Based on the analysis of the momentum distribution in the molecular frame of the two electrons,we found that the asymmetry of the high-energy electrons emitted from both ends of the molecule is greater than that of the ionized electrons from the HOMO orbitals,which leads to the speculation that the N2 O molecule is excited to the autoionization state N2O+* by the absorption of multiple photons after ionizing a HOMO-1 orbital electron in the laser field,and the ionizational dissociation occurs in the laser field that has not yet ended,releasing an electron with very low kinetic energy.We also investigated the Coulomb explosion and dissociation paths of N2 O molecules.Comparing the KER distributions obtained from the Coulomb explosion experimental results of N2 O molecules under the laser of 400 nm linear polarization and 800 nm elliptical polarization,we found that the laser wavelength and ellipticity as well as the laser field intensity affect the dissociation paths.Based on the KER distribution combined with the potential energy surface curce analysis,it is found that the dissociation paths in the 800 nm ellipsoidal field mainly come from the contributions of the ground state 3Σ-and the first excited state 1Δ state;in the 400 nm linearly polarized field it is mainly the contributions of the ground state 3Σ-,the first excited state 1Δ and the second excited state 1Σ+.Further analysis of the KERdependent zox planar angular distribution under the action of the 800 nm elliptical field observes the presence of ion distributions outside the polarization plane,indicating the contribution of π-type orbitals,and corresponds to the presumed obtained electronic states.The ionization order of the two electrons is distinguished according to the momentum magnitude,and the low-energy electron is referred to as the first ionized electron e1 and the high-energy electron is referred to as the second ionized electron e2.The asymmetry of the momentum distribution of the two electrons in the molecular frame is calculated,and it is inferred that their ionization mainly originates from the contribution of molecular HOMO orbitals.Ionization and dissociation are among the most fundamental phenomena in lightmolecule interactions,and the study of these phenomena on ultrafast time scales has advanced many frontiers,such as femtosecond chemistry,attosecond physics,and attosecond chemistry,and will hopefully lead to a deeper understanding of how electrons leave molecules and how molecular bond-breaking occurs,among other fundamental physical issues,leading to a deeper understanding of light-matter interactions.