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The rate constant for quenching of I(P21/2) by O(P3) has been measured for the temperature range 295–360 K. Pulsed laser photolysis of mixtures N2O and I2 was used to examine the kinetics. O(P3) atoms were produced by the photoinitiated reaction sequences N2O+hν→O(D1)+N2 and O(D1)+M→O(P3)+M, while singlet oxygen was generated by the secondary reaction O(D1)+N2O→O2(a 1Δ)+N2. Iodine atoms were produced by I2 photodissociation and from the secondary reactions of I2 with O(P3) atoms. Subsequent excitation of I by O2(a Δ1) led to I(P21/2) formation, with I(P21/2) concentrations monitored using time-resolved 1315 nm emission. The rate constant of the quenching process was determined by fitting a kinetic model to the observed emission traces. Special attention was given to the gas flow conditions. A modest temperature dependence of the quenching rate constant was found, and this was well represented by the equation k=(6.5±1)×10−12(T/300)1.76 cm3 s−1. The room temperature rate constant differs from previous experimental determinations but agrees well with the value determined by modeling of the data from discharge driven oxygen-iodine lasers.

A new kinetic scheme for the dissociation of I 2 by O 2 (a) has been proposed by Azyazov et al. (J. Chem. Phys. 130, 104306/9 (2009)). In principle, the reactions initiated by UV photolysis of N 2 O/I 2 mixtures can be used to probe the chain propagation stage of this dissociation model, and provide additional validation. In the present study, 193 nm laser photolysis of N 2 O/I 2 mixtures was used to initiate secondary chemical reactions and to produce iodine atoms. Singlet oxygen was generated in this system by the fast reaction O( 1 D)+N 2 O→ O 2 (a)+N 2 . Emission spectroscopy and laser induced fluorescence techniques were used to follow the time evolutions of I* and I 2 . The photolysis of N 2 O/I 2 mixtures creates all of the species needed to sustain the chain propagation stage of I 2 dissociation process. However, it was found that the high pressures of N 2 O needed to generate sufficient concentrations of O 2 (a) suppressed the I 2 dissociation process. Computational modeling indicated that suppression of the chain propagation reactions under the conditions examined was consistent with the revised dissociation model.

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