Photodissociation of O3 around 309 nm

Photodissociation reaction of O-3 following ultraviolet photon excitation around the thermodynamic threshold of the dissociation channel of O(D-1) + O-2(a(1)Delta g) at 309.44 nm has been studied under room-temperature and jet-cooled conditions. Both O(D-1) and O(P-3) photoproducts are detected by a technique of vacuum ultraviolet laser-induced fluorescence (VUV-LIF) spectroscopy. Photofragment excitation (PHOFEX) spectra for the O(D-1) and O(P-3) atoms are obtained by scanning the photolysis laser wavelength between 297 and 316 nm while monitoring VUV-LIF signal intensities at 115 and 130 nm for O(D-1) and O(P-3), respectively. From the behavior of the PHOFEX spectra for the O(P-3) and O(D-1) atoms around the threshold into O(D-1) + O-2(a(1)Delta g), the existence of an exit barrier along the O-O-2 dissociation coordinate in the photoexcited electronic state of O-3 is suggested. Analysis of the lint widths in the jet-cooled PHOFEX spectra of O(D-1) and O(P-3) suggests that the quasi-bound states below the barrier and above the threshold have lifetimes of 0.2-0.8 ps. The O(D-1) quantum yield values from the O-3 photolysis are obtained from the PHOFEX spectrum for O(P-3) at 295 K. The O(D-1) quantum yields between 297 and 305 nm are almost independent of the photolysis wavelength (approximate to 0.89), which is smaller than the current NASA/JPL recommendation for atmospheric modeling (0.95). The physical model for O(D-1) formation in the photolysis of O-3 in the wavelength range 305-329 nm is presented, which can quantitatively explain the temperature and wavelength dependence of O(D-1) quantum yield.