  We observed vanishing of the transition dipole moment, interrupting
vibrational ladder climbing (VLC) in molecular systems. We clarified the
mechanism of this phenomenon and present a method to use an additional chirped
pulse to preserve the VLC. To show the effectiveness of our method, we
conducted wavepacket dynamics simulations for LiH dissociations with chirped
pulses. The results indicate that the efficiency of LiH dissociation is
significantly improved by our method compared to conventional methods. We also
revealed the quantum interference effect behind the excitation process of VLC.
