  We have trapped BaF molecules in neon ice, and used laser-induced
fluorescence spectroscopy to map out optical transitions in the trapped
molecules. Our measurements show that the neon lattice does not significantly
perturb certain optical transitions in the trapped molecules. We used one of
these transitions to polarize the electron spins, detect spin flips and measure
hyperfine transitions in the trapped molecules, entirely using lasers. This
demonstration with heavy polar molecules opens up new opportunities for
precision measurements of beyond-standard-model physics.
