LAUSR

Molecular high-order harmonic generation of H and its isotopes is investigated by numerical simulations of the non-Born–Oppenheimer time-dependent Schrodinger equations. The general characteristic of the typical high-order harmonic generation (HHG) spectra for the H molecule indicates that only the odd harmonics can be generated. Here we show that how the initial vibrational states and nuclear dynamics break down this standard characteristic, i.e. a redshift or blueshift of the harmonics appears. We investigate the effect of the initial vibrational states on the redshift or blueshift of the HHG spectrum under trapezoidal laser pulses. The ionization probability and time-frequency analysis are used to illustrate the physical mechanism of the shift of the harmonics. We also show the HHG spectra from the different isotopes of H molecule with different initial vibrational states.