MEASUREMENT OF THE ATOMIC NA(3P) LIFETIME AND OF RETARDATION IN THE INTERACTION BETWEEN 2 ATOMS BOUND IN A MOLECULE

From molecular spectroscopy of the Na-2 purely long range O-g(-), stat e we determine the Na(3P) lifetime and measure the predicted but previ ously unobserved effect of retardation in the interaction between two atoms. Our lifetime tau(P-3/2) = 16.230(16) ns helps to remove a longs tanding discrepancy between experiment and theory. Electron cloud over lap is unimportant in the 0(g)(-) state (R > 55 alpha(0)) and the spec trum is calculated, ab initio, from atomic properties. By measuring th e binding energies the 120 MHz correction due to retardation of the re sonant-dipole R(-3) interaction is confirmed.