  We investigated the high-order harmonic generation (HHG) process of diatomic
molecular ion $\mathrm{H}_2^+$ in non-Born-Oppenheimer approximations. The
corresponding three-dimensional time-dependent Schr\"odinger equation is solved
with arbitrary alignment angles. It is found that the nuclear motion can lead
to spectral modulation of HHG. Redshifts are unique in molecular HHG which
decrease with the increase of alignment angles of the molecules and are
sensitive to the initial vibrational states. It can be used to extract the
ultrafast electron-nuclear dynamics and image molecular structure.
