The rate coefficient for reaction 1, Cl + ClONO2 --> products was meas
ured between 195 and 354 K. Cl atoms were generated by pulsed laser ph
otolysis of Cl-2 in an excess of ClONO2. The temporal profiles of Cl a
tom loss and NO3 product formation were monitored using resonance fluo
rescence and tunable diode laser absorption at 662 nm, respectively, T
he long path absorption system was used to measure k(1) between 200 an
d 298 K while the resonance fluorescence system was employed between 1
95 and 354 K. Thermal decomposition of ClONO2 prevented measurements a
t temperatures greater than 354 K. The two techniques yielded rate coe
fficients which are in excellent agreement, An Arrhenius rate coeffici
ent expression of k(1) = (6.0 +/- 0.4) x 10(-12) exp[(140 +/- 30)/T] c
m(3) molecule(-1) s(-1) and room temperature rate constant of k(1)(298
K) (9.6 +/- 1.0) x 10(-12) cm(3) molecule(-1) s(-1) were derived from
data at T less than or equal to 298 K. The quoted error limits are 2
sigma and include estimated systematic errors. Our results are compare
d with previous measurements, and values of k(1) for atmospheric model
ing are recommended.