We report on the measurement of the scattering properties of ultracold ^{174}Yb bosons in a three-dimensional optical lattice. Site occupancy in an atomic Mott insulator is resolved with high-precision spectroscopy on an ultranarrow, metrological optical clock transition. Scattering lengths and loss rate coefficients for ^{174}Yb atoms in different collisional channels involving the ground state ^{1}S_{0} and the metastable ^{3}P_{0} states are derived. These studies set important constraints for future experimental studies of two-electron atoms for quantum-technological applications L. Franchi et al., |