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[en] The relative efficiencies of the chemical pathways that can lead to the destruction of LiH and LiH⁺ molecules, conjectured to be present in the primordial gas and to control molecular cooling processes in the gravitational collapse of the post-recombination era, are revisited by using accurate quantum calculations for the several reactions involved. The new rates are employed to survey the behavior of the relative abundance of these molecules at redshifts of interest for early universe conditions. We find significant differences with respect to previous calculations, the present ones yielding LiH abundances higher than LiH⁺ at all redshifts.

[en] A theoretical scheme used for controlling efficiently molecular orientation with a few-cycle phase-jump pulse is proposed, with the LiH molecule as an example. It is shown that the molecular orientation can be greatly enhanced by applying this scheme compared to the few-cycle pulse. By optimizing the laser parameters, a high degree of molecular orientation 0.860 is obtained at temperature $T=0\mathrm{K}$. Furthermore, by changing the jump phase and the electric field amplitude of few-cycle phase-jump pulse, the molecular orientation can be improved to some degree. The effect of temperature on molecular orientation is also discussed, the degree of molecular orientation decreases with the increase of temperature. (letter)