  We present the first experimental demonstration of radiation pressure force
deflection and direct laser cooling for barium monohydride (BaH) molecules
resulting from multiple photon scattering. Despite a small recoil velocity (2.7
mm/s) and a long excited state lifetime (137 ns), we use 1060 nm laser light
exciting the $X\rightarrow A$ electronic transition of BaH to deflect a
cryogenic buffer-gas beam and reduce its transverse velocity spread. Multiple
experimental methods are employed to characterize the optical cycling dynamics
and benchmark theoretical estimates based on rate equation models as well as
solutions of the Lindblad master equation for the complete multilevel system.
Broader implications for laser cooling and magneto-optical trapping of
heavy-metal-containing molecules with narrow transition linewidths are
presented. Our results pave the way for producing a new class of ultracold
molecules -- alkaline earth monohydrides -- via direct laser cooling and
trapping, opening the door to realizing a new method for delivering ultracold
hydrogen atoms (Lane 2015 \textit{Phys. Rev. A} 92, 022511).
