The quantum yields for O(1D) production in O3 photolysis between 203 and 320 K, and 289 to 329 nm were measured. A portion of the observed O(1D) quantum yields at wavelengths greater than 310 nm is attributed to a spin-forbidden channel and the variation of quantum yield with temperature is ascribed to photodissociation of vibrationally (or rotationally) excited ozone. Our results yield atmospheric O(1D) production rates larger than those obtained from current recommendations, especially at high solar zenith angles, low temperatures, and large overhead ozone columns. ¿ 1998 American Geophysical Union