A REDETERMINATION OF THE RATE-CONSTANT OF THE REACTION F + HNO3-] HF + NO3

The rate constant k(1) of the reaction F + HNO3 --> HF +/- NO3 at 298 K has been redetermined using two fast flow systems employing different detectors. In the first, growth of NO3 was measured by mass-spectrometric detection of the ion signal at m/e 62. In the other, the decay of F-atoms was measured by following their ESR signal. Uncoated quartz flow tubes were used in both cases. The reactants were kept in the range 12 < [HNO3]/[F] < 140 in all experiments such that pseudo-first-order evaluation of the data was possible and secondary reactions were suppressed. A total of 52 experiments with [HNO3] in the range (2.5-8.2) . 10(13) cm-3 yielded k(1) = (2.2 +/- 0.2) . 10(-11) cm3 molecule-1 s-1, where the error stated is the random error 2-sigma for 96% confidence limit. Model calculations have shown that the systematic error in k(1) due to secondary reactions is less than 2%. The total systematic error in k(1) is estimated to be 10%. The effect of poisoning the flow tube with halocarbon wax was studied in a few experiments and an interpretation for the observation is suggested.