We have observed the photoassociative spectra of colliding ultracold 39K and 85Rb atoms to produce KRb* in all eight bound electronic states correlating with the 39K (4s) + 85RL(Sp1/2 and 5p3/2) asymptotes. These electronically excited KRb* ultracold molecules are detected after their radiative decay to the metastable triplet (a3∑+) state and (in some cases) the singlet (X1∑+) ground state. The triplet (a3∑+) ultracold molecules are detected by two-photon ionization at 602.5 nm to form KRb+, followed by time-of-flight mass spectroscopy. We are able to assign a majority of the spectrum to three states (2(0+), 2(0-), 2(1)) in a lower triad of states with similar C6 values correlating to the K(4s) + Rb (Sp1/2) asymptote; and to five states in an upper triad of three states (3(0+), 3(0-), 3(1)) and a dyad of two states (4(1), 1(2)), with one set of similar C6 values within the upper triad and a different set of similar C6 values within the dyad. We are also able to make connection with the short-range spectra of Kasahara et al. [J. Chem. Phys. 111, 8857 (1999)], identifying three of our levels as v = 61, 62 and 63 of the 11Π ∼ 4(1) state they observed. We also argue that ultracold photoassociation to levels between the K(4s) + Rb (5p 3/2) and K(4s) + Rb (5p1/2) asymptotes may be weakly or strongly predissociated and therefore difficult to observe by ionization of a3∑+ (or X1∑+) molecules; we do know from Kasahara et al. that levels of the 11Π ∼ 4(1) and 21Π ∼ 5(1) states in the intra-asymptote region are predissociated. A small fraction (≤1/3) of the triplet (a3∑ +) ultracold molecules formed are trapped in the weak magnetic field of our magneto-optical trap (MOT).
All Science Journal Classification (ASJC) codes
- Atomic and Molecular Physics, and Optics