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 F-4(7/2), F-4(5/2) and F-4(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 D-6(9/2) 9/2 is determined to be 201(10) mu s 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 mu s. 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.