LONG-RANGE INTERACTION OF THE K-39(4S)-39(4P) ASYMPTOTE BY PHOTOASSOCIATIVE SPECTROSCOPY .1. THE O-G(-) PURE LONG-RANGE STATE AND THE LONG-RANGE POTENTIAL CONSTANTS(K)

This paper reports on a comprehensive study of the long-range interact ion of the K-39(4s) + K-39(4p) asymptotic system. We present a detaile d discussion of the R-dependent angular momentum couplings and correla tion between the Hund's case (a) and case (c) molecular states. Analyt ical expressions for the 16 adiabatic Hund's case (c) long-range poten tial curves are derived including the higher order dispersion forces a nd the effects of retardation. Experimentally, six Hund's case (c) lon g-range molecular states (0(u)(+), 1(g), and 0(g)(-) dissociating to t he 4 S-2(1/2) + 4 P-2(3/2) asymptote and 0(u)(+), 1 g and 0(g)(-) to t he 4 S-2(1/2) + 4 P-2(1/2) limit) are observed with rovibrational reso lution by photoassociative spectroscopy of ultracold K-39 atoms in a h igh density magneto-optical trap (MOT). Among the six observed long-ra nge states, the upper 0(g)(-) ''pure long-range'' state has negligible short-range chemical exchange contributions and the measured molecula r binding energies (v = 0-26) are used to precisely determine the long -range potential constants of the 4s + 4p interaction. We determine: C -3(Pi) = 8.436(14) a.u., C-3(Sigma) = 16.872(28) a.u., C-6(Pi) = 6272( 94) a.u., and C-6(Sigma) = 9365(141) a.u. Molecular constants for the three special pure long-range states, the 0(g)(-) and 1(u) (dissociati ng to the 4 P-2(3/2) limit and with potential minimum) and the 1(u) (d issociating to the 4 P-2(1/2) and with potential maximum), are reporte d. The internal consistency of the theoretical model used in this work is confirmed by the excellent agreement between the long-range potent ial curve of the 1(g) state obtained in present work (from the 0(g)(-) srate) and the long-range portion of the RKR potential curve of the 1 (1) Pi(g) state previously determined by conventional molecular spect roscopy. The radiative lifetime of the K 4p state derived from the n i s also in excellent agreement with a recent fast-beam dipole-dipole in teraction constant C-3(Pi) is also in excellent agreement with a recen t fast-beam measurement. (C) 1997 American Institute of Physics. measu rement.