Spectroscopy of Na2 by photoassociation of laser-cooled Na

We have observed the spectrum of long range molecular states of singly excited Na2 formed by photoassociation during ultracold associative ionization collisions of laser-cooled Na atoms. The low kinetic energy of the collision allows us to obtain very high resolution spectra and to observe states close to the dissociation limit. The spectrum shows regular vibrational series characteristic of the 1/R3 long range portion of the 1g potential (asymptotically S1/2+P3/2) as well as molecular hyperfine structure within these peaks. We extract potential parameters and compare with recent theory.