We have examined the metal/medium interface effects on the optical absorption due to Mie plasmon resonance of sodium nanoclusters passivated with CH4-nCln (n = 1-4) molecules. The redshifted bands are observed around 600 nm in each Na/CH4-nCln aerosol generated by the gas-aggregation technique with a reactant nozzle (GATRN). The peak energies are also redshifted with increasing the reactant-gas flow rates. The dielectric coated metal-particle model predicts that the sodium nanoclusters passivated with CH4-nCln form in the aerosols and that the peak redshifts are due to the dielectric-shell growth and static charge transfer at metal/medium interface.