Absolute rate coecients …k1 † for the deactivation of electronically excited oxygen atoms, O…1 D2 †, by phosgene …Cl2 CO† have been measured as a function of temperature over the range 194± 425 K. The results are well described by the Arrhenius expression k1 …T † ˆ 2X04 × 10-10 exp…‡27aT † cm3 molecule-1 s-1 . The reported values for k1 …T † are considerably lower than the values currently recommended for use in modeling stratospheric chemistry. The yield of