The pressure dependence of the Herzberg photoabsorption continuum of oxygen

The origin of pressure dependence in the dipole forbidden Herzberg continuum of oxygen is discussed in terms of the formation of oxygen dimers and the collision of free molecules. The small temperature dependence of the pressure coefficient indicates that the collisions of free molecules have the dominant influence. Consideration of the selection rules applying to the Herzberg systems and the strengths of the associated band systems leads to the conclusion that the pressure dependence results from enforced dipole transitions in the Herzberg III (A′³Δ_u−X³Σ_g^-) system.