Theoretical Exploration of the Isotopic Effect on Molecular High-Order Harmonic Generation

The isotopic effect on the generation of the molecular high-order harmonics is studied by numerically solving the one-dimensional time-dependent Schrödinger equation when the model hydrogen molecule ions/hydrogen deuterium molecule ions are exposed to an intense laser pulse. To explain the effect more clearly, not only the ionization probabilities but also the electron–nuclear probability density distributions and time-frequency profiles are calculated. The results show that more intense harmonics are generated in the asymmetric diatomic molecule ions/hydrogen deuterium molecule ions than those of hydrogen molecule ions. Moreover, the interference minimum in the harmonic spectra is investigated by adjusting the laser intensity and the initial vibrational state. It is shown that the interference minimum is sensitive to the laser intensity and the initial vibrational level for hydrogen molecule ions; in contrast, it is only dependent on the initial vibrational level for hydrogen deuterium molecule ions.