Photodissociation of O3 in the Hartley Band. Reactions of O(1D) and O2(1Σg+) with O3 and O2

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Abstract
The ultraviolet photolysis of O3 in the presence and in the absence of O2 has been investigated in the wavelength region ∼ 2375–2625 Å using flash photolysis and kinetic emission spectroscopy with a time resolution high enough to allow unambiguous identification of photodissociation products. The production of O(1D) was established by observing the forbidden 1D → 3P emission at 6300 Å. The decay of the emission provided a value of the rate constant for the O(1D)–O3 reaction of (2.5 ± 1) × 10−10 cm3 molecule−1·sec−1 at 25°C. Analysis of the O(1D) decay showed that the rate of chain reactions in which O(1D) could be reproduced must be smaller than the O(1D)–O3 quenching rate by more than an order of magnitude. No emission was observed from O2(1Σg+) when O3 alone was photolyzed, indicating that the primary yield for O2(1Σg+) production is smaller than 1/20 of the O(1D) production. O(1D) was very efficiently quenched when N2 and O2 were added. O2(1Σg+) was observed by the 1Σg+ → 3Σg− emission when O3–O2 mixtures were photolyzed. The emission disappeared when N2 was added. The O2(1Σg+) production and decay rates were measured at various O3 and O2 concentrations. The results indicated that O2(1Σg+) was formed by energy transfer from O(1D) to ground state O2. The decay of the 1Σg+ emission provided a value of the rate constant for the O2(1Σg+)–O3 quenching of (2.5 ± 0.5) × 10−11 cm3 molecule−1·sec−1. The relative quenching rate of O(1D) by O3 and O2 was about 5, yieding an O(1D)–O2 rate constant of 5 × 10−11 cm3 molecule−1·sec−1 with an uncertainty of a factor of 2. The dependence of the 1Σg+ emission on the O2 pressure showed that the primary quantum yield of O2(1Σg+) is at least 20 times smaller than that of O(1D) , in agreement with the previous result.

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