FINE-STRUCTURE PREDISSOCIATION OF ULTRACOLD PHOTOASSOCIATED K-39(2) MOLECULES OBSERVED BY FRAGMENTATION SPECTROSCOPY

We report the first observation of fragmentation spectra of the fine-s tructure predissociated long-range 1(g) and 0(n)(+) (b (II0+u)-I-3) st ates of ultracold (T < 1 mK) K-39(2) molecules. The 1(g) state prediss ociates via the curve crossing at long range (R similar to 73 Angstrom ) with the repulsize 0(g)(+) state. The 0(u)(+) state, however, predis sociates predominantly through molecular fine-structure mixing at shor t range with the b (II1u)-I-3 component. Our technique of fragmentatio n spectroscopy is a sensitive and selective tool for ultracold photoas sociation and fine-structure-changing collisions.