Kinetic study on the photoabsorption process of gaseous O2 dimol at 630 nm in a wide pressure range

The visible light absorption of gaseous O2 dimol at 630 nm was measured in the pressure region of 0.04–90 atm. The intensities measured at high pressures did not agree with the values extrapolated from the data obtained at low pressures. A kinetic analysis assuming the equilibrium between the dimol and free O2 monomers was performed. All the data are well reproduced by the model using the 630 nm absorption cross-section of (5.6 ± 3.3) × 10−24 cm2 molecule−1 and the dissociation equilibrium constant of (6.8 ± 4.2) × 1021 molecules cm−3. The critical distance between the O2 molecules in the dimol is discussed on the basis of the equilibrium constant determined.