The methylmetal hydride compounds of zinc, cadmium, and mercury have been formed by the insertion of the excited metal atom into methane and trapped in an argon matrix. The excitation of the zinc, cadmium, or mercury atom required to promote insertion can be effected through the use of a heated microwave discharge source of the metal by the action of its resonance radiation or by irradiation into the P-3(1) metal excited state. The methylmetal hydride compounds have been characterized by infrared spectroscopy and their identities authenticated by H-2 and C-13 enrichment. The mechanism of insertion has been investigated by selective photolysis studies of the matrix-isolated reactants. The insertion product formed by the reaction of excited mercury atoms with ethane has also been studied.