The separation of deuterium from hydrogen have been carried out by infrared multiphoton dissociation in trifluoroacetaldehyde with 9.6umP(26) line from a TEA CO2 laser. The separation coefficient was 200 and the deuterium content of final composition was 80% from photolysis of gaseous GFBCHO containing 2.4% of GF3CDO. Adding helium could increase separation effect but oxygen would induce a chain reaction and lose selectivity.