Primary Processes in Ozone Photolysis

Abstract

The photolysis of O3 dissolved in liquid Ar at 87°K has been studied at 2537 Å and at wavelengths near 3130 Å. Quantum yields of O3photodecomposition were determined for O3 concentrations ranging from 5×10−4 to 0.3 mole/liter at 2537 Å and 0.03 to 0.67 mole/liter at 3130 Å. Disappearance of O3 is attributed to the reactions O 3 → lim φI abs O 2 + O ( 1 D), O ( 1 D)+ O 3 →2 O 2, where Φ is the quantum yield of O(1 D) formation at a given wavelength. The limiting photodecomposition quantum yield at high O3 concentration is about 2 at 2537 Å and about ½ at 3130 Å. Quantum yields were also determined at several wavelengths in the interval 2970 to 3340 Å for the photo‐exchange reaction O 3 + 36 O 2 → 52 O 3 + O 2 . The foregoing studies, together with previous work, show that the O(1 D) quantum yield in O3photolysis is unity below 3000 Å but falls to a value of 0.4±0.15 in the 3130‐Å region. The exchange experiments show that the total quantum yield of atomic oxygen, including O(1 D) and O(3 P), retains a constant value of unity throughout the wavelength range studied, with onset of O(3 P) formation occurring at 3000 Å. From these results the rate of O(1 D) production in the lower atmosphere is calculated to be 1.2±0.5 pphm/h (pphm is parts per hundred million), based on an assumed O3 concentration of 10 pphm and a solar zenith angle of 45°.