Precise determination of the dipole matrix element and radiative lifetime of the K-39 4p state by photoassociative spectroscopy

Rovibrational levels (v = 0-30) of the 0(g)(-) ''pure long-range'' state of K-39(2) are observed by photoassociative spectroscopy of ultracold potassium atoms prepared in a high-density magneto-optical trap. The measured molecular binding energies are used to precisely determine the long-range dipole-dipole potential constant C-3(II) of the K(4s) + K(4p) asymptote and the radiative lifetime of the 4p state. We determine C-3(II) = -5.456(9) zJ nm(3) (-8.445(14) a.u.), tau(4 P-2(3/2)) = 26.34(5) ns, and tau(4 P-2(1/2)) = 26.69(5) ns. Our result is a significant improvement in precision over previous lifetime measurements and agrees well with the recent fast-beam experiment [U. Volt and H. Schmoranzer, Phys. Scr. T65, 48 (1996)].