The formation of specific target states in Na-2(+) is investigated using phase-locked femtosecond pulse sequences. The pulse sequences generate customized vibrational wave packets whose motion can be interpreted using classical physics. It is shown that, if two vibrational wave packets are initially excited at either end of the vibrational coordinate, changing the initial phase difference between them can have a profound effect on the subsequent dynamics. In particular, the choice of phase differences (2 pi, pi, -pi/2 or pi/2) has a dramatic effect on the dynamics around the times of the second and fourth order partial revivals. The results are interpreted quantitatively using knowledge of the phase differences between components of fractional revivals evolving from a single wave packet. Finally, we discuss a novel detection technique for monitoring vibrational wave packet dynamics in molecular cations, which combines phase-modulated detection methods borrowed from Rydberg electron wave packet experiments and zero-kinetic energy pulsed-field ionization borrowed from high-resolution spectroscopy.