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

Motivated by Yung and Miller's [1997] suggestion that N2O is isotopically fractionated during UV photolysis in the stratosphere, we have studied the photolysis rates of the ^(14)N^(15)N^(16)O and ^(15)N^(14)N^(16)O structural isotopomers. In this study, we follow the concentrations of these compounds with FTIR spectroscopy during photolysis at 213 nm. When fitted to a Rayleigh fractionation model, the observations yield single‐stage enrichment factors of ϵ(^(14)N^(15)N^(16)O / ^(14)N^(14)N^(16)O) = −73 ± 5 per mil and ϵ(^(15)N^(14)N^(16)O / ^(14)N^(14)N^(16)O) = −41 ± 10 per mil. As predicted by Yung and Miller [1997], the photolysis rate of ^(15)N^(14)N^(16)O is faster than ^(14)N^(15)N^(16)O at this wavelength. The magnitude of the observed fractionation, however, is significantly larger than predicted