Fractionation of ¹⁴N¹⁵N¹⁶O and ¹⁵N¹⁴N¹⁶O 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 ¹⁴N¹⁵N¹⁶O and ¹⁵N¹⁴N¹⁶O 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(¹⁴N¹⁵N¹⁶O / ¹⁴N¹⁴N¹⁶O) = −73 ± 5 per mil and ϵ(¹⁵N¹⁴N¹⁶O / ¹⁴N¹⁴N¹⁶O) = −41 ± 10 per mil. As predicted by Yung and Miller [1997], the photolysis rate of ¹⁵N¹⁴N¹⁶O is faster than ¹⁴N¹⁵N¹⁶O at this wavelength. The magnitude of the observed fractionation, however, is significantly larger than predicted.