Formation of ultracold ⁷Li⁸⁵Rb molecules in the lowest triplet electronic state by photoassociation and their detection by ionization spectroscopy

We report the formation of ultracold ⁷Li⁸⁵Rb molecules in the a³Σ⁺ electronic state by photoassociation (PA) and their detection via resonantly enhanced multiphoton ionization (REMPI). With our dual-species Li and Rb magneto-optical trap apparatus, we detect PA resonances with binding energies up to ∼62 cm^-1 below the ⁷Li 2s ²S_1/2 + ⁸⁵Rb 5p ²P_1/2 asymptote. In addition, we use REMPI spectroscopy to probe the a³Σ⁺ state and excited electronic 3³Π and 4³Σ⁺ states and identify a³Σ⁺ (v″ = 7-13), 3³Π (v_Π′ = 0-10), and 4³Σ⁺ (v_Σ′ = 0-5) vibrational levels. Our line assignments agree well with ab initio calculations. These preliminary spectroscopic studies on previously unobserved electronic states are crucial to discovering transition pathways for transferring ultracold LiRb molecules created via PA to deeply bound rovibrational levels of the electronic ground state.