We have obtained spectra of the high-lying vibrational levels of the $1^3$${\mathrm{\Sigma }}_{\mathit{g}}^{+}$ state of ${}_{}{}^6{}_{}{}^{}\mathrm{Li}_2^{}{}_{}{}^{}$ via photoassociation of ultracold ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ atoms confined in a magneto-optical trap. The $1^3$${\mathrm{\Sigma }}_{\mathit{g}}^{+}$ state of the diatomic molecule correlates to a 2${\mathit{S}}_{1/2}$ state atom plus a 2${\mathit{P}}_{1/2}$ state atom. The long-range part of the molecular interaction potential for this state depends on the 2P atomic radiative lifetime. By calculating the energy eigenvalues of a model potential for the $1^3$${\mathrm{\Sigma }}_{\mathit{g}}^{+}$ state and fitting them to the experimentally measured vibrational levels, we have extracted a value for the 2P lifetime of 26.99±0.16 ns. The precision is currently limited by the accuracy of a region of the model potential provided by ab initio calculations.

• Received 1 August 1994

DOI:https://doi.org/10.1103/PhysRevA.51.R871