Theoretical Investigation of the Laser-Induced Ionization–Fragmentation Dynamics of H₂ Associated with Ionization Timings

The theoretical investigation on the laser-induced ionization-fragmentation dynamics is very challenging, all dynamics processes from neutrality to ionization and then to fragmentation of molecular ions must be considered. In this work, we develop a quantum time-dependent wave packet evolution method to simulate the entire process of laser-induced ionization-fragmentation of H₂. Our investigation specifically delves into the influence of laser ionization timing of neutral H₂ on molecular kinetic energy release and orientation of H₂⁺. The present simulations show that H₂⁺ generated at the rising edge of the pulse tends to fragment perpendicular to the laser polarization direction, whereas those formed at the falling edge predominantly fragment parallel to it. Further, the ionization timing of neutral H₂ also directly determines the dissociation probabilities of different vibrational energy levels by changing the dressed potentials of H₂⁺, resulting in a smaller kinetic energy release for H₂⁺ generated at the rising edge of pulse. These results expose the time-dependent molecular fragmentation dynamics within a single pulse, and provide a novel methodology for studying time-resolved fragmentation dynamics, namely by analyzing the correlation between ionic energy and orientation to realize time resolution.