Wavelength and temperature dependence of the absolute O(1D) production yield from the 305–329 nm photodissociation of ozone

O ( 1 D) and O(3Pj) photofragments produced in the photodissociation of ozone in the wavelength range 305–329 nm both at 295 and 227 K have been detected directly using a technique of laser induced fluorescence (LIF) in the vacuum ultraviolet (vuv). Photofragment excitation (PHOFEX) spectra for both species have been measured by scanning the photodissociation laser wavelength whilst monitoring vuv-LIF at 115 nm [O(1D)] and 130 nm [O(3Pj)]. After applying suitable corrections for the relative detection sensitivities, suitably weighted combinations of these PHOFEX spectra were found to provide a quantitative match to the parent O3 absorption spectrum both at 295 and 227 K, thereby providing a method of determining both the wavelength and temperature dependence of the absolute O(1D) quantum yield, Φ1D(λ,T). Hot band excitation of internally excited O3 molecules and dissociation via the spin-allowed channel yielding O(1D)+O2(a 1Δg) products makes the dominant contribution to the quantum yield Φ1D(λ,T) in the wavelength range 310–320 nm. For λ>320 nm, however, both the Doppler profiles of the nascent O(1D) atoms and the temperature dependence of the O(1D) yield indicate that the O(1D) atoms must arise predominantly via the spin-forbidden channel yielding O(1D)+O2(X 3Σg−). The analysis allows a first determination of the absolute branching to this channel (Φ∼0.08) following O3 photolysis in the wavelength range 318–329 nm. The present work highlights remaining deficiencies in the latest NASA/JPL recommendations regarding the wavelength and temperature dependence of the O(1D) yield resulting from O3 photolysis at λ>320 nm.