Formation of deeply bound ultracold LiRb molecules via photoassociation near the Li 2S1/2+Rb 5P3/2 asymptote

Abstract

We present spectra of ultracold Li7Rb85 molecules in their electronic ground state formed by spontaneous decay of weakly bound photoassociated molecules. Beginning with atoms in a dual-species magneto-optical trap, weakly bound molecules are formed in the 4(1) electronic state, which corresponds to the B1Π state at short range. These molecules spontaneously decay to the electronic ground state and we use resonantly enhanced multiphoton ionization to determine the vibrational population distribution in the electronic ground states after spontaneous emission. Many of the observed lines from the spectra are consistent with transitions from the X1Σ+ ground electronic state to either the B1Π or the D1Π electronic state that has been previously observed, with levels possibly as low as X1Σ+(v''=2) being populated. We do not observe decay to weakly bound vibrational levels of the X1Σ+ or a3Σ+ electronic state in the spectra. We also deduce a lower bound of 3900 cm−1 for the dissociation energy of the LiRb+ molecular ion.