Coherent spin-rotational dynamics of oxygen super rotors

TL;DR

This study investigates the rotational dynamics of oxygen molecules in extreme rotational states using advanced spectroscopy and optical centrifuge techniques, revealing enhanced robustness of rotational wave packets and unique spin-rotation coherence decay behaviors.

Contribution

It demonstrates the excitation of oxygen molecules to very high rotational states and analyzes the resulting spin-rotation coherence decay, highlighting differences from non-magnetic molecules.

Findings

Achieved rotational quantum numbers up to N=109 in high-density ensembles.

Observed faster rotational decoherence in oxygen compared to nitrogen at high N.

Identified a potential different relaxation mechanism in paramagnetic gases.

Abstract

We use state- and time-resolved coherent Raman spectroscopy to study the rotational dynamics of oxygen molecules in ultra-high rotational states. While it is possible to reach rotational quantum numbers up to $N \approx 50$ by increasing the gas temperature to 1500 K, low population levels and gas densities result in correspondingly weak optical response. By spinning O$_2$ molecules with an optical centrifuge, we efficiently excite extreme rotational states with $N\leqslant 109$ in high-density room temperature ensembles. Fast molecular rotation results in the enhanced robustness of the created rotational wave packets against collisions, enabling us to observe the effects of weak spin-rotation coupling in the coherent rotational dynamics of oxygen. The decay rate of spin-rotation coherence due to collisions is measured as a function of the molecular angular momentum and explained in terms of the general scaling law. We find that at high values of $N$, the rotational decoherence of oxygen is much faster than that of the previously studied non-magnetic nitrogen molecules. This may suggest a different mechanism of rotational relaxation in paramagnetic gases.