Many different processes produce nitrous oxide (N₂O), a potent greenhouse gas. Measuring the ratio of heavy and light nitrogen isotopes (¹⁵N/¹⁴N) for the non-exchangeable central and outer N atoms of N₂O helps to distinguish sources of N₂O. To accurately calculate the position-specific isotopic preference, we developed an expansion of the widely used Rayleigh model. Application of our new model to simulated and experimental data demonstrates its improved accuracy for analyzing N₂O synthesis.