Studies on fundamental processes on mass-independent isotope fractionation of sulfur compounds in photochemical rea ctions

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To investigate the interaction between UV photolysis of SO_2 and mass-independent isotope fractionation of sulfur (MIF-S) signatures, absorption cross sections of all S-substituted SO_2 isotopologues (^<32>SO_2, ^<33>SO_2, ^<34>SO_2, and ^<36>SO_2) were determined between 183 and 330 nm in every 0.05 nm using a double-beam spectrometer. The cross sections of SO_2 are very different for the four isotopologues from 183 to 230 nm. The MIF-S signature of SO_2 by irradiation using a 193 nm ArF laser is well explained by different photolysis rate of SO_2 using a kinetic model depending on cross section of each isotopologue. Absorption cross sections of O-substituted SO_2 isotopologues (^<32>S^<16>O^<18>O, ^<32>S^<18>O_2 ; ^<34>S^<16>O^<18>O,^<34>S^<18>O_2) were also estimated to clarify oxygen isotope variations associated with SO_2 photolysis.