Persistent Ground-State Planar Alignment of Iodine Molecule through Resonant Excitation

We demonstrate the generation of a persistent planar molecular alignment by subjecting a relatively warm gas sample to a resonant femtosecond laser pulse. By optically probing I₂ molecules in their vibronic ground states, we observe a persistent delocalization of their axes near the plane orthogonal to the field direction. This phenomenon is attributed to the one-photon resonant excitation, primarily removing molecules from the thermal ground-state distribution that are initially aligned along the field, i.e., those with small projection of their rotational angular momentum along the field.