Collisional decoherence and rotational quasirevivals in asymmetric-top molecules

We demonstrate the observation of quasiperiodic revivals out to 27 ps in an impulsively aligned asymmetric-top molecule, sulfur dioxide (SO2), at high sample temperature and density (295 K, 0.5 bar). We find that the asymmetric top exhibits a strong correlation between population alignment and population lifetime (r=0.97), in accordance with the trend observed in linear molecules. We use a linear birefringence measurement fit to a full quantum simulation of the asymmetric rotor and are able to separately measure both the population (T1) and coherence (T2) lifetimes of the rotational wave packet. Additionally, we observe a high rate of elastic decoherence (T2∗=9.6ps) and attribute this to long-range interactions mediated by the permanent dipole of the SO2 molecule. We propose the use of birefringence measurements to study intermolecular interactions in a coherent ensemble, as a step toward using field-free alignment to investigate reaction dynamics and dissipative processes.