Intersystem crossing in sulphur dioxide
Abstract
Excitation spectra of the fluorescence of SO2 and of the SO2 photosensitised phosphorescence of biacetyl have been recorded between 250 and 325 nm, and the rates of decay of the fluorescence and the generation and decay of the biacetyl phosphorescence have been monitored following pulsed laser excitation at (295–300 nm). Rate coefficients for the fluorescence quenching by SO2, N2, CF4, SF6 and cyclohexane and for triplet energy transfer to biacetyl have been determined, together with relative rate coefficients for collisionally induced intersystem crossing by N2, CF4, SF6 and SO2; SF6 and SO2 are far more efficient than CF4 or N2.
The results indicate a single fluorescent species at pressures 2 N m–2(emitting to wavelengths 500 nm) and a common precursor to both the fluorescent 1B1 state and the triplet states populated through collisionally induced intersystem crossing. Arguments against the postulate of a very low-lying 3B2 state are discussed, and evidence for the population of non-emitting triplet states is presented.