High resolution photoassociation spectroscopy of the ${}^6$Li${}_2$ $1^3{\Sigma }_g^{+}$ state

Abstract

We present experimental observations of seven vibrational levels $v^{\prime }=20-26$ of the $1^3{\Sigma }_g^{+}$ excited state of Li${}_2$ molecules by the photoassociation (PA) of a degenerate Fermi gas of ${}^6$Li atoms. For each vibrational level, we resolve the rotational structure using a Feshbach resonance to enhance the PA rates from p-wave collisions. We also, for the first time, determine the spin-spin and spin-rotation interaction constants for this state. The absolute uncertainty of our measurements is $\pm 0.00002$ cm${}^{-1}$ ($\pm 600$ kHz). We use these new data to further refine an analytic potential for this state.