  Probing the real time dynamics of a reacting molecule remains one of the
central challenges in chemistry. In this letter we show how the time-dependent
wavefunction of an excited-state reacting molecule can be completely
reconstructed from resonant coherent anti-Stokes Raman spectroscopy. The method
assumes knowledge of the ground-state potential but not of any excited-state
potential, although we show that the latter can be computed once the
time-dependent excited-state wavefunction is known. The formulation applies to
polyatomics as well as diatomics and to bound as well as dissociative excited
potentials. We demonstrate the method on the Li$_2$ molecule with its bound
first excited-state, and on a model Li$_2$-like system with a dissociative
excited state potential.
