Reactions of scandium and yttrium monoxide molecules (ScO and YO) with monochloromethane have been studied in solid argon by infrared absorption spectroscopy and density functional theoretical calculations. The metal monoxide molecules were prepared by laser-evaporation of bulk metal oxide targets. The results show that the ground state scandium and yttrium monoxide molecules reacted with CH3Cl to form two MO(CH3Cl) (M = Sc, Y) complex isomers spontaneously oil annealing. Broad-band UV-visible irradiation initiated the addition of the Cl-C bond to the M=O bond to form the CH3OMCl molecule and the addition of the C-H bond to the M=O bond to give the CH2ClMOH isomer, both of which are more stable than the MO(CH3Cl) complex structures. The CH2ClMOH molecule was predicted to involve agnostic interaction between the chlorine atom and the metal atom.