Xenon Sensitized Photolysis of Carbon Dioxide

The xenon-sensitized photolysis of CO2 has been examined and contrasted with the direct photolysis at the 1470-Å Xe resonance line. In the Xe-sensitized system, the following results were obtained: the quantum yield for CO production φCO equals 2 at low pressure of CO2; φCO decreases toward unity upon addition of several gases whose relative efficiencies are as follows: CO2=1.00, Xe=0.90, He=0.14, Kr=0.06, and C2F6=0; complete recovery of O2 (O2 / CO = 0.50) is always achieved. The principal reactions required to explain these results are: Xe+hv→Xe*, Xe*+CO2→Xe+CO+O(1D)†, O(1D)†+CO2→CO3*, CO3*→CO+O2, CO3*+M→O(3P) or O(1D)+CO2+M. where O(1D)† represents electronically excited atomic oxygen containing excess kinetic energy. The high efficiency of He in this system (0.14) compared to that previously established for O(1D) with no excess kinetic energy (0.02) lends support to participation of O(1D)† in the Xe-sensitized photolysis of CO2.