Orientation dependence of harmonic emission from vibrating HeH2+ versus HeT2+: Effects of a permanent dipole.

We study high-order harmonic generation (HHG) from the oriented asymmetric molecule HeH2+ and its isotopic variant HeT2+ in strong few-cycle laser pulses, by numerically solving the non-Born-Oppenheimer time-dependent Schrödinger equation. Our simulations show that the influence of nuclear motion on HHG of the asymmetric system is dependent on the molecular orientation and the laser parameters. At relatively weak laser intensities, the HHG yields of HeH2+ are higher than those of HeT2+ for the parallel orientation and the situation reverses for the perpendicular orientation. However, at high laser intensities, they become comparable for the parallel case. With a developed simple HHG model that considers the influences of nuclear motion on all of the ionization, propagation, and recombination processes of HHG, we show the permanent dipole of the system plays an important role in these phenomena. Our results shed light on the complex dynamics of the asymmetric system in strong laser fields. [ABSTRACT FROM AUTHOR]