Complete Reconstruction of the Wavefunction of a Reacting Molecule by Four-Wave Mixing Spectroscopy

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.