(color online) (a) Variations of maximal orientation degree of LiH (black) and HBr (red) with THz field frequency, where E01=6.0×107V·cm−1, E02=2.0×105V·cm−1, σr = 4 ps, T= 0 K. (b) Populations of rotational states of LiH and HBr at ωTHz = 0.5 THz with other parameters being the same as those in panel (a).