Low-temperature kinetics of reactions of the OH radical with propene and 1-butene studied by a pulsed Laval nozzle apparatus combined with laser-induced fluorescence

The kinetics of the reactions of the OH radical with propene and 1-butene are studied at T = 103 K. The low-temperature environment is provided by a pulsed Laval nozzle supersonic expansion of nitrogen with admixed radical precursor and reactant gases. The gas number density and temperature distributions in the flow are characterized by both dynamic pressure measurements and laser-induced fluorescence (LIF) spectroscopy of OH radicals excited in the (1,0) band of the A(2)Sigma (+) - X(2)Pi (i), transition. For the kinetic measurements, the OH radical decay profiles in the presence of reactants are monitored by LIF. The rate constants of the reactions of OH with propylene and 1-butene are measured at T = 103 K to be (0.81 +/- 0.18) x 10(-10) and (1.24 +/- 0.27) x 10(-10) cm(3) molecule(-1) s(-1), respectively. The observed negative temperature dependences of the rate constants for both reactions studied by the pulsed Laval nozzle system show good agreement with both low-temperature and high-temperature kinetic data available in the literature.