Recent research interests have been raised in uncovering and controlling ultrafast dynamics in excited neutral molecules. In this work we generalize the Monte Carlo wave packet (MCWP) approach to XUV-pump–IR-probe schemes to simulate the process of dissociative double ionization of ${\mathrm{H}}_2$ where singly excited states in ${\mathrm{H}}_2$ are involved. The XUV pulse is chosen to resonantly excite the initial ground state of ${\mathrm{H}}_2$ to the lowest excited electronic state of ${}^1{{\mathrm{\Sigma }}_u}^{+}$ symmetry in ${\mathrm{H}}_2$ within the Franck-Condon region. The delayed intense IR pulse couples the excited states of ${}^1{{\mathrm{\Sigma }}_u}^{+}$ symmetry with the nearby excited states of ${}^1{{\mathrm{\Sigma }}_g}^{+}$ symmetry. It also induces the first ionization from ${\mathrm{H}}_2$ to ${{\mathrm{H}}_2}^{+}$ and the second ionization from ${{\mathrm{H}}_2}^{+}$ to ${\mathrm{H}}^{+}+{\text{H}}^{+}$. To reduce the computational costs in the MCWP approach, a sampling method is proposed to determine in time the dominant ionization events from ${\mathrm{H}}_2$ to ${{\mathrm{H}}_2}^{+}$. By conducting a trajectory analysis, which is a unique possibility within the MCWP approach, the origins of the characteristic features in the nuclear kinetic energy release spectra are identified for delays ranging from 0 to 140 fs and the nuclear dynamics in the singly excited states in ${\mathrm{H}}_2$ is mapped out.

• Received 13 December 2017
• Revised 26 March 2018

DOI:https://doi.org/10.1103/PhysRevA.97.043426

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society