Energy Levels and Transition Rates for Laser Cooling Os⁻ and a General Approach to Produce Cold Atoms and Molecules

High-resolution photoelectron energy spectra of osmium anions are obtained using the slow-electron velocity-map imaging method. The energy levels of excited states ⁴F_7/2, ⁴F_5/2 and ⁴F_3/2 of Os⁻ are determined to be 148.730(13), 155.69(15), and 176.76(13) THz or 4961.09(41), 5193.4(49), and 5896.1(42) cm⁻¹, respectively. The lifetime of the opposite-parity excited state ${}^6{D}_{9/2}^{\mathrm{o}}$ is determined to be 201(10) μs using a cold ion trap, about 15 times shorter than the previous result 3(1) ms. Our high-level multi-configuration Dirac–Hartree–Fock calculations yield a theoretical lifetime 527 μs. Our work shows that the laser cooling rate of Os⁻ is as fast as that of Th⁻. The advantages of Os⁻ are its near-IR range cooling transition and simple electronic structure, which make Os⁻ a promising candidate for laser cooling of negative ions. We propose a general approach to produce cold atoms and molecules based on the sympathetic cooling of negative ions in combination with a threshold photodetachment.