Temperature-dependence study of the gas-phase reactions of atmospheric NO3 radicals with a series of amides

The reactions of the nitrate radical with N,N-dimethylformamide (k1); N,N-dimethylacetamide (k2); N,N-dimethylproprionamide (k3) and 1-methyl-2-pyrrolidinone (k4), have been investigated using an absolute rate method. Experiments were performed using a laser photolysis technique coupled with UV-Visible absorption detection over the pressure range (100–200)±2 Torr and the temperature range (277–353)±2 K. This study provides the first determination of NO3 rate constant for reactions with four amides over a large temperature range. NO3 radical was produced by photolysis of the gas mixture F2/N2/HNO3/amide at 351 nm and detected at 662 nm where its cross section is well known. Four amides, showing a systematic variation of substitute, have been studied. The Arrhenius expressions (in cm3 molecule−1 s−1) were as follows:k1=(1.06×10-11exp((-1600±300)/T),k2=(2.82×10-11exp((-1900±200)/T),k3=(12.52×10-11exp((-2700±300)/T),k4=(2.42×10-11exp((-1500±100)/T).The obtained rate coefficients are compared with the reactivity towards the OH radicals. The results are also discussed in terms of the structure–reactivity relationship. In addition, the atmospheric implications are discussed.