MEASURING GAS-PHASE CHLORINE ATOM CONCENTRATIONS - RATE CONSTANTS FORCL+HN3, CF3I, AND C2F5I

A convenient method is reported for the measurement of gas-phase Cl at om concentrations in the 10(11)-10(13) atoms cm(-3) range in a flow re actor. The titration reaction with vinyl bromide is used to measure th e absolute CI atom concentration, and the relative Cl atom concentrati on is monitored by the HCl(v) infrared emission intensity produced by the reaction of Cl atoms with hydrogen sulfide. A microwave discharge through dilute flows of Cl-2, CCl4, CFCl3, and CF2Cl2 in Ar were chara cterized as sources of Cl atoms in the flow reactor. The elementary ra te constants for reaction of Cl atoms with HN3, CF3I, and C2F5I were m easured as (1.1 +/- 0.3) x 10(-12), (5.1 +/- 1.5) x 10(-13), and (3.9 +/- 0.8) x 10(-12) cm(3) molecule(-1) s(-1), respectively, at 300 K. T hese rate constants were obtained after adjustment of the apparent rat e constants for secondary reactions.