The mechanism of the collision-induced enhancement of the a1Δg-X3Σg- and b1Σg+ → a1Δg radiative transitions of O2

Large sets of literature data on the enhancement of the O-2 emissions a(1)Delta(g) --> X(3)Sigma(g)(-) in solution and b(1)Sigma(g)(+) --> in the gas phase have been analyzed. Second-order rare constants have been interpreted with respect to molecular parameters such as collision frequency, molecular size, and molecular polarizability of the collider. It is shown that the transition moments of both collision-induced radiative transitions are directly proportional to the molecular polarizability of the collider, if the effects of collider size and collision frequency are removed. A transient shift of electron density from the collider MOs into the pi(g,x) and pi(g,y) molecular orbitals of O-2 occurs, which induces electric dipole character into the b --> a transition. Because of the strong spin-orbit coupling of O-2, the a --> X transition profits proportionally from the enhancement of the b --> a transition by intensity borrowing.