Photosensitised production of singlet oxygen, O<inf>2</inf>^7z.ast;(a¹Δ<inf>g</inf>) , in the unique 'heavy-atom' solvent, supercritical fluid xenon. Pressure dependence of electronic to vibrational energy conversion during quenching of O<inf>2</inf>^*(a¹Δ<inf>g</inf>) by xenon and by ground state oxygen

Abstract

Photosensitised generation of singlet oxygen, O2*(a1Δg), in supercritical xenon, SCF-Xe at 325 K is reported for the first time. Rate constants for quenching by ground state oxygen, and by xenon, vary from 8.9±0.3 to 13±1×102and from 7±1 to 4.4±0.5dm3mol-1s-1, respectively, as the pressure increases from 7.8 to 44 MPa. The measured decay constant shows little temperature dependence in the range 295-325 K at 29.6 MPa. The extrapolated lifetime of O2*(a1Δg), expected in the absence of O2(X3Σg-), in SCF-Xe, at 325 K and 8.8 MPa is 22±3ms. Explanations for observed variations are proposed and factors governing the decay of singlet oxygen in SCF-Xe are discussed. © 2001 Elsevier Science B.V.