GAS-PHASE CHEMILUMINESCENCE STUDY OF CHEMICALLY ACTIVATED TETRAMETHYL-1,2-DIOXETANE FORMED FROM THE REACTION OF O-2(1-DELTA-G) WITH 2,3-DIMETHYL-2-BUTENE

Chemically activated tetramethyl-1,2-dioxetane has been prepared by the reaction of O2(1DELTA(g)) with 2,3-dimethyl-2-butene at temperatures of 450 to 775 K and a pressure of 0.25 Torr. The observed product of the reaction was excited 1npi* (S1) acetone, which was identified by chemiluminescence spectra of the acetone (S1 --> S0) transition. Neither acetone (T(i)) nor any other excited states were observed under the above conditions. The temperature dependence of the chemiluminescence gave an activation energy for the cycloaddition reaction of 8610 +/- 200 (1 sigma) cal/mol. The quantum yield for acetone (S1) was 4 X 10(-3) per reactive collision; its (1 sigma) error is estimated a +/- a factor of 3. Chemiluminescence spectra taken at 02(3SIGMA(g)-) partial pressures greater than 2 Torr showed formaldehyde (S1 --> S0) bands. This is attributed to the well-known hydrocarbon "cool flame" mechanism, due to the presence of methyl radical formed by the thermal decomposition, in two steps, of 2,3-dimethyl-3-hydroperoxy-1-butene, another product path for the title reaction. This is the first report on the chemically activated decomposition of tetramethyl-1,2-dioxetane.