The Research Of Coulomb Explosion Imaging Of Water Molecule And Its Isotope Effect

The interaction between water molecule and strong femtosecond laser induces rich ultrafast dynamics,Coulomb explosion imaging technique offers a robust method to detect those interesting processes.In this thesis,we studied the dissociative multiple ionization of water and also its Coulomb explosion(CE),the molecular structure before explosion has been extracted,and the isotope effect within this process has been discussed.We compared the kinetic energy release(KER)between linearly and circularly polarized light,and discussed the effect of vibrational mode and bond stretching during the Coulomb explosion.We also tried to measure the two ions and two electrons in coincidence to study the two electron dynamics during the sequential double ionization of molecule.First,we studied double ionization and two-body CE,two maximums are observed at 0 and 90 degree,and the KER at 0 degree is higher than 90 degree.This phenomenon relies on the laser polarization.The possible origin is the laser alignment effect and the multiple orbital ionization.The momentum sum of two fragments along laser polarization shows the shoulder structure,which indicates two electrons ejected in the same direction.The yield ratio between two channels from HOD molecule is about 6.8 for linearly polarized light,but it decreased to 4.6 for circularly polarized light.This indicates O-H bond is much easier to stretch and dissociation compare to the O-D bond.And this ratio can be controlled by changing the laser polarization.Moreover,using three-body coincidence technique,we extracted the bond angle of water molecule before the Coulomb explosion,this angle extended from 80 to 170 degree,which indicates very complex structure dynamics during the dissociative ionization,the three vibrational mode of water all can play a role for the dynamics.Within the circularly polarized light,the suppression for the small angle has been confirmed,which may be due to the large contribution of double ionization induced by heavy scattering under linear polarization leading to the rapid coulomb explosion without time for molecular deformation.The KER for circularly light is higher than linearly light,which is in contrast with the linear molecule.The water molecule prefers to symmetric stretch within circularly polarized light,but asymmetric stretch is very important for linearly polarized light.We also approved the isotope effect in asymmetric stretching process of water molecule.