Production of ultracold 85Rb133Cs molecules in the lowest ground state via the B1Π1 short-range state.

Abstract

We investigate the production of cold 85Rb133Cs molecules in the lowest vibronic level of the ground electronic state via the B1Π1 short-range state. The photoassociation (PA) spectra of the B1Π1 state, including newly observed transition to 2 vibronic levels, are obtained by high sensitivity time-of-flight mass spectrometry. Based on these PA spectra, the harmonic and anharmonic constants of vibronic states are obtained, resulting in predicted vibronic energies with an uncertainty of 1-2 cm-1. The B1Π1 (v = 3) state is found to have the maximum production rate for ground-state molecules with a value of 3(1) × 104 s-1, which is 3 times larger than the value via the previously studied 23Π0+ (v = 10, J = 0) state with two-photon cascade decay. The populations of J = 0, 1, and 2 rotational levels of X1Σ+ (v = 0) state molecules formed via the B1Π1 (v = 3, J = 1) state are measured to be around 20%, 40%, and 20%. To quantify the coupling strength between the B1Π1 (v = 3) state and X1Σ+ (v = 0) state, the transition dipole moment between them is measured to be 7.2(2) × 10-3ea0, which is also 3 times larger than the value between the 23Π0+ (v=10) state and X1Σ+ (v = 0) state, meaning the B1Π1 (v = 3) state has a stronger coupling with the X1Σ+ (v = 0) state. Our detailed measurements provide relevant parameters for investigation on direct stimulated Raman adiabatic passage transfer between the atomic scattering state and molecular bound state for 85Rb133Cs molecules.