Energetic materials have important applications in many fields, including defence, security and civil engineering. However, the microscopic mechanisms of their reactions are still poorly understood. Nitrogen, is the main mass donor molecule released after the explosion of energetic materials. In this study, we measured the CARS relaxation curves of N₂ molecules by femtosecond time-resolved coherent anti-Stokes Raman scattering (fs-CARS) spectroscopy at room temperature. And we use a spectral estimator that enables time-frequency super-resolution, called the superlet transform, to perform time-frequency resolved spectral analysis of the complex molecular dynamics process of N₂. The more obvious rotational modes of N₂ molecules evolving with time are observed, and rotational coupling constants such as B_e are obtained. The experimental results are in good agreement with the O and S branches in the N₂ rotational Raman spectra obtained from theoretical simulations. The spectral analysis technique provides a concise solution for studying the rovibrational coupling and energy transfer mechanisms during molecular collision reactions.
 

ultrafast time-resolved spectroscopy, superlet, rovibrational coupling, energy transfer, molecular dynamics