The rate coefficient for the quenching of N(²D) by O(³P) has been measured by using an afterglow source and resonance absorption detection for N(²D). Quenching by known concentrations of O atoms, generated by NO titration of a nitrogen discharge, was compared with the quenching by O2, N2O, and CO2, for which the rate coefficients are well known. The rate constant for N(²D) quenching by O(³P) derived in this manner is (1.8 ± 0.6) × 10−12cm³ molecule−1s−1at 315°K. A small increase with temperature in this rate constant relative to that for O2was found, consistent with an activation energy of 1 ± 0.5 kcal/mol fo