Mixtures of O3 with excess N2O were photolysed in the wavelength region 290 - 335 nm using monochromatic light with a band width of 4 nm. The resulting primary product atomic singlet oxygen, O(1D), in reacting with N2O produces in part NO which subsequently reacts with O3 giving rise to a weak infrared chemiluminescence. The emission was monitored with a cooled photomultiplier. The emission intensity is directly proportional to the rate of O(1D) production and it has been utilised to derive the relative O(1D) quantum yield as a function of wavelength between 295 and 320 nm. The data were normalised to a quantum yield of unity of 300 nm and corrections were applied to reduce the error resulting from the spectral band width of photolysing radiation. The O(1D) quantum yields show a temperature dependence. At 298 K the quantum yield is unity up to 305 nm, then declines to zero at 319 nm. At the dissociation limit, taken to occur at γ = 310.3 nm, the quantum yields is 0.57, i. e. considerably below unity. The implications of this result as well as the tail toward longer wavelengths and the temperature dependence are discussed. Ozone absorption cross sections are also reported.