Fractionation of (NNO)-N-14-N-15-O-16 and (NNO)-N-15-N-14-O-16 during photolysis at 213 nm

Motivated by Yung and Miller's [1997] suggestion that N2O is isotopically f ractionated during UV photolysis in the stratosphere, we have studied the p hotolysis rates of the (NNO)-N-14-N-15-O-16 and (NNO)-N-15-N-14-O-16 struct ural isotopomers. In this study, we follow the concentrations of these comp ounds with FTIR spectroscopy during photolysis at 213 nm. When fitted to a Rayleigh fractionation model, the observations yield single-stage enrichmen t factors of epsilon((NNO)-N-14-N-15-O-16 / (NNO)-N-14-N-14-O-16) = -73 +/- 5 per mil and epsilon((NNO)-N-15-N-14-O-16 / (NNO)-N-14-N-14-O-16) = -41 /- 10 per mil. As predicted by Yung and Miller [1997], the photolysis rate of (NNO)-N-15-N-14-O-16 is faster than (NNO)-N-14-N-15-O-16 at this wavelen gth. The magnitude of the observed fractionation, however, is significantly larger than predicted.