Coherent Ro-vibrational Revivals in a Thermal Molecular Ensemble

We report an experimental and theoretical study of the evolution of vibrational coherence in a thermal ensemble of nitrogen molecules. Rotational dephasing and rephasing of the molecular vibrations is detected by coherent anti-Stokes Raman scattering. The existence of weak ro-vibrational coupling and the discrete nature of the rotational bath lead to a whole new class of full and fractional ro-vibrational revivals. Following the rich dynamics on a ns time scale with sub-ps resolution enables us to determine the rotational constant $\gamma_e$, as well as the intensity ratio between the different Raman transitions.