Measurements of quantum yields of bromine atoms in the photolysis of bromoform from 266 to 324 nm

Abstract

The quantum yield for the formation of bromine atoms in the photolysis of bromoform, CHBr_3, has been measured between 266 and 324 nm. For 303 to 306 nm the quantum yields are unity within the experimental uncertainty of the measurements. At longer wavelengths, where the bromoform cross sections decrease rapidly, an apparent trend to slightly lower quantum yields is probably the result of systematic and random errors or incorrect CHBr_3 absorption cross sections. Support for a unit quantum yield for all wavelengths longer than 300 nm comes from the recent theoretical calculations of Peterson and Francisco. At 266 nm the bromine atom quantum yield is 0.76 (±0.03), indicating that at least one additional dissociation channel becomes important at shorter wavelengths. For modeling of the troposphere, it is recommended that a quantum yield of unity be used for wavelengths of 300 nm and longer.