Photolysis of SO 2 in the presence of foreign gases. V. Sensitized phosphorescence of biacetyl

Abstract

SO 2 was irradiated in the presence of biacetyl at 3020 Å and 25°C. The SO 2-sensitized phosphorescence of biacetyl was monitored both in the absence and presence of N 2, CO, CO 2, N 2O, H 2O, and thiphene. The results show that two triplet states of SO 2 must be involved to explain the yields of biacetyl phosphorescence. Neither of these states has the properties of the emitting triplet state of SO 2 ( 3B 1 or 3SO 2). In particular, neither of the two SO 2 triplets is quenched by N 2, CO, CO 2, or N 2O. One of the states, SO 2**, is quenched by H 2O, but not by thiophene, whereas the reverse is true for the other state, SO 2≢. The emitting 3SO 2 state is quenched by all six gases, and very markedly by thiophene. The state SO 2≢ is rapidly quenched by biacetyl and accounts for the sensitized phosphorescence at low biacetyl pressure. At higher biacetyl pressures (∼ 1 Torr), its phosphorescence is enhanced because of quenching of SO 2**. The SO 2** state has the same properties as the triplet state responsible for chemical reactioin between photoexcited SO 2 and CO.