Vibrational branching ratios and hyperfine structure of 11BH and its suitability for laser cooling

*Correspondence: M. R. Tarbutt, Blackett Laboratory, Centre for Cold Matter, Imperial College London, Prince Consort Road, London SW72AZ, UK e-mail: [email protected] The simple structure of the BH molecule makes it an excellent candidate for direct laser cooling. We measure the branching ratios for the decay of the A1 (v ′ = 0) state to vibrational levels of the ground state, X1 +, and find that they are exceedingly favorable for laser cooling. We verify that the branching ratio for the spin-forbidden transition to the intermediate a3 state is inconsequentially small. We measure the frequency of the lowest rotational transition of the X state, and the hyperfine structure in the relevant levels of both the X and A states, and determine the nuclear electric quadrupole and magnetic dipole coupling constants. Our results show that, with a relatively simple laser cooling scheme, a Zeeman slower and magneto-optical trap can be used to cool, slow and trap BH molecules.