Knowledge Bank

Photo association spectroscopy provides a precision, high resolution tool for probing long range interatomic interactions in the ground and excited states of diatomic molecules cooled and trapped atomic species. A number of groups are now exploiting one- and two-color photo association spectroscopy of trapped atom. Photo association is a free-bound transition induced by light between colliding ground stale atoms and a bound vibrational-rotational level of the molecule formed by the two atoms. High resolution is possible because of the very small spread in thermal energy of the atoms at $\le 0.001$ K. The asymmetric line shapes of the spectral lines show the influence of natural broadening and the quantum properties of the ground state wave function. Analysis of spectra of the $0g-$ state of the $Na2$ molecule at NIST has been used to determining the long range resonant dipole interaction strength between ground and excited Na atoms, yielding the most accurate value to dale of the $Na2p3/2$ atomic lifetime, as well as observation of relativistic retardation corrections to the long range inter atomic interaction. IN addition, since these spectra probe the ground state wave function the $T\to 0$ limit, we have determined the scattering length for collision of two Na atoms in the $F=1,M=-1$ hyperfine state. This is a critical parameter in the theory of Bose-Einstein condensation of this species.