Hyperfine-Structure-Induced Depolarization of Impulsively Aligned $\rm I_2$ Molecules

TL;DR

This study investigates how hyperfine interactions affect the rotational alignment of I2 molecules after laser excitation, revealing complex substructures and mean alignment decay explained by quantum modeling.

Contribution

It introduces a quantum mechanical model linking hyperfine coupling to observed depolarization and complex revival structures in impulsively aligned molecules.

Findings

Experimental alignment shows non-periodic substructure.

Quantum model accurately reproduces experimental results.

Hyperfine interactions cause depolarization effects.

Abstract

A moderately intense $450$ fs laser pulse is used to create rotational wave packets in gas phase $\rm{I_2}$ molecules. The ensuing time-dependent alignment, measured by Coulomb explosion imaging with a delayed probe pulse, exhibits the characteristic revival structures expected for rotational wave packets but also a complex non-periodic substructure and decreasing mean alignment not observed before. A quantum mechanical model attributes the phenomena to coupling between the rotational angular momenta and the nuclear spins through the electric quadrupole interaction. The calculated alignment trace agrees very well with the experimental results.