Collisional Deactivation of O2(1Δg) by Solvent Molecules. Comparative Experiments with 16O2 and 18O2

Abstract

AbstractPhosphorescence spectra of natural singlet oxygen 16O2(1Δg) and its heavier isotope 18O2(1Δg) have been recorded in several O2(1Δg) weakly deactivating solvents. Lifetimes of singlet oxygen were determined for both isotopes in 21 solvents. From these data rate constants kXY of deactivation of singlet oxygen by terminal oscillators X—Y of the solvent molecules are calculated revealing a graduated isotope effect of 1.0 ≤ 16kXY/18kXY ≤ 1.9. The unexpectedly low isotope effect points to the important role of overtone excitations of X—Y during O2(1Δg) deactivation. A modified collisional deactivation model including overtone excitation of the energy accepting oscillator reproduces the experimental findings: the tremendeous graduation of kXY of almost 5 orders of magnitude, the heavy atom effect, the O2 isotope effect and the very weak temperature effect on kXY.