High resolution FFT spectroscopy of spin-rotation wavepackets in N₂⁺ following strong-field ionization

When nitrogen molecules are ionized by femtosecond pulses at 800 nm, post-ionization coupling launches wavepackets in several low-lying cationic states. We probe these bound-state wave packets using a dissociative third harmonic probe and use FFT spectroscopy to identify the states involved with rotational resolution. We find broad rotational excitation in the three lowest cationic states. The coupling of spin and electronic angular momentum to rotational angular momentum is also apparent over the 200 ps scan. We also isolate the momentum distributions from specific two-state rotational coherences to understand the role of rotational motion in the dissociation process.