(color online) Time evolution of molecular orientations of (a) LiH and (b) HBr at T = 0 K (solid line), 10 K (dash line), and 20 K (dotted line), ((c), (d)) corresponding rotational population before excitation, and ((e), (f)) the corresponding rotational population after excitation. The parameters are adopted to be σ_r = 4 ps, ω THz = 18 cm − 1 , E 01 = 1.0 × 10 8 V · cm − 1 , and E 02 = 2.0 × 10 5 V · cm − 1 .