An improved method and apparatus for the production of oxygen radicals that may be used for cleaning portions high vacuum instruments. The apparatus comprises a VUV vacuum ultraviolet light source or lamp placed in an irradiation chamber for the photo disassociation of oxygen in communication with the main chamber on a specimen chamber port or inside the specimen chamber. Air or other oxygen-containing gas is admitted to the irradiation chamber for photo disassociation. The VUV source radiates UV wavelengths below 193 nm that are used to disassociate oxygen in the gas to create the oxygen radicals and the pressure is held high enough for complete absorption of the light. The oxygen radicals are differentially pumped into main chamber at pressure below 100 milliTorr to prevent recombination to clean hydrocarbons from the surfaces instrument by oxidation to volatile oxide gases. The oxide gases are then removed by the vacuum pump.
