  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
${\rm A}^{1}\Pi (v'=0)$ state to vibrational levels of the ground state, ${\rm
X}^{1}\Sigma^{+}$, and find that they are exceedingly favourable for laser
cooling. We verify that the branching ratio for the spin-forbidden transition
to the intermediate ${\rm a}^{3}\Pi$ 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.

Atomic Physics