Collisional decoherence and rotational quasirevivals in asymmetric-top molecules

Abstract

We demonstrate the observation of quasiperiodic revivals out to 27 ps in an impulsively aligned asymmetric-top molecule, sulfur dioxide $({\mathrm{SO}}_{2})$, 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 $({\mathrm{T}}_{1})$ and coherence $({\mathrm{T}}_{2})$ lifetimes of the rotational wave packet. Additionally, we observe a high rate of elastic decoherence $({\mathrm{T}}_{2}^{*}=9.6\phantom{\rule{4.pt}{0ex}}\mathrm{ps})$ and attribute this to long-range interactions mediated by the permanent dipole of the ${\mathrm{SO}}_{2}$ 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.