The kinetics of biacetyl phosphorescence sensitized in 2875 Å‐irradiated SO 2 –biacetyl–added gas (CO 2 , CO, N 2 ) mixtures. The nature of the SO 2 excited states formed at high added gas pressures

The quantum yields of sensitized biacetyl phosphorescence emission have been determined for SO 2 –biacetyl–CO 2 , SO 2 –biacetyl–N 2 , and SO 2 –biacetyl–CO mixtures irradiated at 2875 Å. Series of experiments were made at various SO 2 , biacetyl, and added‐gas concentrations (up to 4 × 10 ‐2 M ). The kinetic data show an “excess” biacetyl emission which requires the participation of some undefined excited state or isomer of SO 2 in addition to the emitting singlet ( 1 SO 2 ) and triplet ( 3 SO 2 ) states of SO 2 . These results confirm the experimental observations of Cehelnik et al. [12] and Wampler et al. [9] who reported that an “excess” quantum yield of CO 2 occurred in 3130 Å‐irradiated SO 2 ‐CO mixtures at high CO pressures. The kinetic analysis of the data is most consistent with the hypothesis of Wampler et al.; the nonreactive, undefined excited state or high‐energy isomer of SO 2 , designated here as X, is formed in part as 1 SO 2 is quenched: 1 SO 2 + M → (SO 2 M) (1); 1 SO 2 + M → 3 SO 2 + M (2); 1 SO 2 + M → X + M (3). X itself does not transfer energy to biacetyl. It decays largely by a nonradiative first‐order process at low pressures, X → SO 2 (5), but it generates 3 SO 2 by collisional perturbation at high pressures, X + M → 1 SO 2 + M (4). In terms of this mechanism, the following rate constant ratios are derived from the present study: k 2 /( k 1 + k 2 + k 3 ) = 0.020 ± 0.010 (M = CO 2 ), 0.021 ± 0.010 (N 2 ), 0.019 ± 0.010 (CO); k 3 /( k 1 + k 2 + k 3 ) = 0.14 ± 0.02 (M = CO 2 ), 0.085 ± 0.012 (CO), 0.11 ± 0.02 (N 2 ); and k 5 / k 4 (mole/l) = 0.020 ± 0.004 (M = CO 2 ), 0.016 ± 0.003 (CO), 0.021 ± 0.005 (N 2 ).