Output pulse observations are presented for a helium‐diluted CO2laser pumped by VV (vibration‐vibration) energy transfer from vibrationally excited DF produced by the D2&sngbnd;F2chain reaction. Flash photolysis of the F2served to initiate the reaction. A 290‐cm3reaction chamber containing a 0.5‐atm mixture with mole ratio D2:F2:CO2:He = 0.33:1:8:10 gave a single‐pulse output energy of 2.8 J. Relative to the amount of D2present in the reaction chamber, this corresponds to a chemical efficiency greater than 5%.