Photosensitised production of singlet oxygen, O2*(a1Δg), in the unique `heavy-atomʹ solvent, supercritical fluid xenon. Pressure dependence of electronic to vibrational energy conversion during quenching of O2*(a1Δg) by xenon and by ground state oxygen

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±1×102 and from 7±1 to 4.4±0.5 dm3 mol−1 s−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±3 ms. Explanations for observed variations are proposed and factors governing the decay of singlet oxygen in SCF-Xe are discussed.