Research On Ultrafast Dynamic Imaging Of Ring Molecules Under Femtosecond Laser Field

Ultrafast imaging research of strong field ultrafast atomic and molecular dynamics is a frontier research topic.After the interaction between polyatomic molecules and femtosecond laser,multiple ionization and Coulomb explosion occur,and based on the momentum correlation of fragments,the ultrafast structure changes can be reconstructed,which is called molecular Coulomb explosion imaging.Using time-resolved Coulomb explosion imaging method to study ultrafast optical molecular dynamics quickly and reveal the ultrafast structural changes of molecules and ions,and further realize the molecular film capture at the atomic distance scale,this paper focuses on the complex ring organic molecules benzene,1,3-cyclohexadiene,cyclohexene and cyclohexane.Coulomb explosion imaging measurement and data analysis of the system were carried out,and time resolved Coulomb explosion imaging technology was developed.The dissociation ionization induced by strong field ionization was systematically studied.We have established and developed a coincidence imaging system of time-resolved molecular Coulomb explosion.A time-resolved study has been carried out on the ultrafast dynamics of the typical ring molecule benzene dissociation.The.C₃H₃ channel has a new channel at a delay of more than 500fs and KER below2eV,indicating that the molecular symmetry dissociation reappears after 500 fs.The results show that the probability of Coulomb explosion depends on the configuration of the molecule.The energy of the hydrogen transfer channel broadens obviously at the time zero point,and more low energy ions appear.The signal intensity of the hydrogen transfer channel presents a weak oscillation with time.The molecular three-body Coulomb explosion imaging can also reflect the structural changes and time scales of ring opening process.Time resolved photo-dissociation and Coulomb explosion imaging are helpful to study the dynamic behavior of excited states of molecular ions,and lay the foundation for further imaging of molecular excited state ultrafast structures.The four kinds of molecular channel resolved different properties of fragments yield.The degree of fragmentation depends on the electronic state and geometric structure of the ring molecules.Based on the cold target recoil ion momentum imaging spectrometer?COLTRIMS?,we realized the dissociation ionization and Coulomb explosion kinetic information of four kinds of ring molecules by combining the coincidence imaging and the pumping detection scheme of femtosecond infrared laser.Four kinds of molecular channel resolved fragment ion yields showed different properties.The degree of fragmentation depends on the electronic state and geometric structure of the ring molecules.Compared with the other three molecules,the degree of fragmentation of benzene molecules is the smallest and the degree of fragmentation of cyclohexane molecules is the highest.The yield of the two-body dissociation channel of the ring molecules is regular distribution,and the asymmetric two body dissociation rate is higher than the symmetry dissociation.The CH₃⁺channels containing hydrogen transfer are the strongest.The two body Coulomb explosion yield and KER?Kinetic-energy Release?analysis show that four molecules have hydrogen transfer processes and their yields depend on the properties of the molecules.The hydrogen transfer process is widespread in the two body Coulomb explosion of the ring molecules,and the yield of CH₃ channels in the saturated ring C₆H₁₂ decreases.It is proved that the existence of double bonds enhances the hydrogen transfer process.The two-dimensional momentum distribution of Coulomb explosion process is related to the orbital symmetry of molecules.Combined with the HOMO distribution of the highest occupied orbit,it shows that the pi orbital and the sigma orbit lead to different angular distribution characteristics of molecules.