Photosensitised production of singlet oxygen, O-2(*)(a(1)Delta g), in the unique 'heavy-atom' solvent, supercritical fluid xenon. Pressure dependenceof electronic to vibrational energy conversion during quenching of O-2(*)(a(1)Delta g) by xenon and by ground state oxygen

Photosensitised generation of singlet oxygen, O-2* (a(1) Delta (g)), in sup ercritical xenon, SCF-Xe at 325 K is reported for the first time. Rate cons tants for quenching by ground state oxygen, and by xenon, vary from 8.9 +/- 0.3 to 13 +/- 1 x 10(2) and from 7 +/- 1 to 4.4 +/- 0.5 dm(3) mol(-1) s(-1 ), respectively, as the pressure increases from 7.8 to 44 Wa. The measured decay constant shows little temperature dependence in the range 295-325 K a t 29.6 Wa. The extrapolated lifetime of O-2*(a(1)Delta (g)), expected in th e absence of O-2(X(3)Sigma (-)(g)), in SCF-Xe, at 325 K and 8.8 MPa is 22 /- 3 ms. Explanations for observed variations are proposed and factors gove rning the decay of singlet oxygen in SCF-Xe are discussed. (C) 2001 Elsevie r Science BN. All rights reserved.