摘要： Laser cooling is a well-established technique for the creation of ensembles of ultracold neutral atoms or positive ions. This ability has opened many exciting new research fields over the past 40 years. However, no negatively charged ions have been directly laser cooled because a cycling transition is very rare in atomic anions. Efforts of more than a decade currently have La? as the most promising candidate. We report on experimental and theoretical studies supporting Th? as a new promising candidate for laser cooling. The measured and calculated electron affinities of Th are, respectively, 4901.35e48T cm?1 and 4832 cm?1, or 0.607 690(60) and 0.599 eV, almost a factor of 2 larger than the previous theoretical value of 0.368 eV. The ground state of Th? is determined to be 6d37s2 4Fe 5=2. The consequence of this there are several strong electric dipole transitions between the bound levels arising from configurations 6d37s2 and 6d27s27p in Th?. The potential laser-cooling transition is 2So 3=2 with a wavelength of 2.6 μm. The zero nuclear spin and hence lack of hyperfine structure in Th? reduces the potential complications in laser cooling as encountered in La?, making Th? a new and exciting candidate for laser cooling.