Rate coefficient for deactivation of O(21S) by H2O

We have measured the absolute rate coefficient for collisional deactivation of O(21S) by H2O. The experimental method involved electron-beam irradiation of mixtures of H2O and O2 in high-pressure Ar; the irradiation energy initially deposited in the argon transferred to O2 to produce O(21S) atoms. Observation of the O(21S) lifetime as a function of H2O pressure permitted deduction of a quenching coefficient of 1.27±0.15×10−10 cm3 s−1.