Molecular vibrational state distributions in collisions

Experimental vibrational spectra of H₂ in the collision with a proton at 30 eV in the laboratory frame are compared to results from calculations using the electron nuclear dynamics. Nuclei are treated classically. Interpreting the classical vibration in terms of a coherent state yields quantum vibrational levels reproducing the experimental results. This result indicates that collision dynamics, including vibrational excitation, does not require numerical-grid wave packet dynamics for an understanding of the fundamental mechanisms involved, but that the concept of coherent state can provide a simple and accurate method to resolve product vibrational states from fully dynamical classical trajectories.