Ultrafast Coulomb Explosion Dynamics Of NH₃ Molecules And Clusters In Strong Laser Fields

Coulomb explosion study of molecules and molecular clusters under irradiation of ultrafast intense laser field has played an important role in the molecular structure imaging and understanding of dissociation dynamics,so it has been widely concerned by researchers.A deep understanding of fragmentation kinetics can improve the accuracy of molecular structure imaging based on the Coulomb explosion method,and provide assistance in the study of the correlation between fragment ions and the dissociation mechanism of their molecules or clusters.In this thesis,we using the COLTRIMS and the ion-ion multi-body coincidence measurement device,studied the NH₃ molecule and its clusters??NH₃?_n,n=2-4?ionization and dissociation kinetics,reconstruction of structural imaging under a strong femtosecond laser field which are by detecting the momentum and kinetic energy distribution of related fragment ions.We first studied the continuous dehydrogenation process of a single NH₃ molecule,and extracted three coulomb explosion channels with different valence states.By comparing the momentum distribution of different debris ions,it was speculated that there might be three kinds of electric dissociation paths in NH₂⁺-H⁺channel.Combined with the kinetic energy correlation between the fragment ions,we observed that there is a sequential ionization process of H⁺in the NH⁺-H⁺-H⁺channel.Then,the Coulomb explosion occurs,which leads to the asymmetric stretching of the two H⁺.By comparing the momentum and kinetic energy distribution of the four-body channel,we found that the N⁺-H⁺-H⁺-H⁺four-body channel was formed directly by the Coulomb explosion.By comparing the kinetic energy changes of the ion fragments of the three dehydrogenation channels,we speculate that the configuration of the NH₃molecule has undergone a transformation from a regular tetrahedron to a planar structure during ionization and dissociation.Further,we studied the proton transfer process of the?NH₃?_n cluster,and found that the two-body,three-body and four-body?NH₃?_n cluster configurations obtained in the experiment were linear,equilateral triangle and square,which were consistent with the cluster structure with the lowest energy calculated theoretically.Therefore,the proton transfer process had no significant influence on the cluster structure of?NH₃?_n.In the experiment,we observed the formation of?NH₃?₄ clusters,and observed the proton transfer between adjacent molecules and the relative intermolecular proton transfer process.It is estimated that the relative intermolecular proton transfer process is more difficult to occur,so the number of ions that can be detected should be less,which is consistent with our experimental observation results.