Inverse temperature dependencies in the quenching of singlet oxygen O2(1Σ+<i>g</i>) by CO2 and N2O studied with a discharge flow/shock tube

Abstract

The rates of quenching of O2(1Σ+g) by CO2 and N2O have been measured at 293 K and between 600 and 1300 K by studying the time-resolved emission in a discharge flow/shock tube experiment. For CO2, the quenching constant rises slightly from 2.09±0.23×108 dm3 mol−1 s−1 at 293 K to a maximum and then falls to 1.44×107 dm3 mol−1 s−1 at 1300 K. The behavior for N2O is similar, rising slightly from 5.89±0.25×107 dm3 mol−1 s−1 at 293 K and falling to 1.65×107 dm3 mol−1 s−1 at 1250 K. The detailed results are given in Figs. 5 and 8. The low temperature results agree well with previous work. A comparison is made of the decline in rate with the model of Parmenter, which unfortunately does not fit, although his suggested correlation of cross section with well depth is reasonable at room temperature. It is suggested that various temperature dependences found for these and other quenchers indicate that curve crossing occurs in those systems close to the potential energy minimum and so makes the rates very sensitive to the nature of the quenching molecule. An additional emission is found at longer times in the N2O system, which is attributed to chemiluminescence from NO2 formed by decomposition of N2O.