FORMYL CHLORIDE - UV ABSORPTION CROSS-SECTIONS AND RATE CONSTANTS FOR THE REACTIONS WITH CL AND OH

Spectroscopic and kinetic properties of gaseous formyl chloride (CHClO) were studied in large reaction chambers. The near-UV absorption spectrum was investigated with a spectral resolution of 0.7 nm. The UV spectrum is similar to that of formaldehyde but shifted to lower wavelengths by about 45 nm. The absorption maximum lies between 250 and 260 nm, with an absorption cross section of (6.0 ± 1.2) × 10-20 cm2 at 260 nm. The reactions of CHClO with OH, Cl, and H2O were studied by relative rate methods. For the rate constant of the reaction CHClO + OH → products, an upper limit of ≤3.2 × 10-13 cm3/s was determined at room temperature. The reaction CHClO + Cl → products was studied at atmospheric pressure as a function of temperature between 266 and 322 K. In this temperature range the rate constant is represented by the Arrhenius expression 1.39 × 10-11 exp(-7.2 ± 1.4 kJ·mol-1/RT) cm3/s. From these data, a lower limit of about 1 month is derived for the tropospheric lifetime of CHClO with respect to photolysis and reactions with OH and Cl. Actually, the tropospheric lifetime of CHClO may be limited by hydrolysis as only an upper limit of 5 × 10-22 cm3/s could be determined for the rate constant of the gas-phase reaction of CHClO with water vapor at 298 K, which corresponds to a lower limit of its lifetime of about 2 h at typical tropospheric conditions. © 1990 American Chemical Society.