The visible light absorption of gaseous O-2 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 O-2 monomers was performed. All the data are well reproduced by the model using the 630 nm absorption cross-section of (5.6 +/- 3.3) x 10(-24) cm(2) molecule(-1) and the dissociation equilibrium constant of (6.8 +/- 4.2) x 10(21) molecules cm(-3). The critical distance between the O-2 molecules in the dimol is discussed on the basis of the equilibrium constant determined. (C) 2010 Elsevier B. V. All rights reserved.