Isotope effects on the ionization of hydrogen molecular ions in strong laser fields

Abstract

Isotope effects on the ionization of hydrogen molecular ions in strong laser fields are studied by numerically simulating the time-dependent Schr\odinger equation. Though the isotopes of hydrogen molecular ions have identical Born-Oppenheimer potential curves, the distinct ionization scenarios are observed for single-photon, multiphoton, and tunneling ionization. For multiphoton and tunneling ionization, the ionization rate of ${{\mathrm{H}}_{2}}^{+}$ is larger than that of ${{\mathrm{D}}_{2}}^{+}$ and ${{\mathrm{T}}_{2}}^{+}$. The ratio of the intensity-dependent tunneling ionization probabilities of ${{\mathrm{H}}_{2}}^{+}$ (${{\mathrm{D}}_{2}}^{+}$) and ${{\mathrm{T}}_{2}}^{+}$ can be qualitatively explained by the adiabatic tunneling theories if a few-femtosecond ultrashort pulse is used. For tens of femtosecond laser pulses, the nuclear movement is unavoidable and the time-dependent Schr\odinger equation simulation is necessary in order to calculate the ionization probability accurately. For single-photon ionization, the electron-nuclei joint energy spectra are distinct though the total ionization probabilities are similar. The elastic constant of potential curves can be retrieved by comparing the single-photon-induced electron-nuclei joint energy spectra of different isotopic molecular ions, which offers a potential technique to image molecules.