Transient resonance Raman spectroscopy and density functional theory investigation of iso-polyhalomethanes containing bromine and/or iodine atoms

We report additional transient resonance Raman spectra and density functional theory computations for the products formed following ultraviolet photoexcitation of solution phase polyhalomethanes containing bromine and/or iodine atoms. We show that the iso-polyhalomethane photoproduct is responsible for the intense transient absorption band observed in the 350-470 nm region after ultraviolet excitation of polyhalomethanes in the solution phase. We examine the trends and correlation in the density functional theory optimized geometry and intense electronic absorption transition in the 350-470 nm region for the iso-polyhalomethanes containing bromine and/or iodine atoms. We explore the chemical reactivity of the iso-polyhalomethane species using density functional theory computations for the reaction of iso-CH2Br-Br with ethylene as an example. Our results and comparison with experimental data in the literature indicate that the iso-polyhalomethane species is most likely the methylene transfer agent in the cyclopropanation reactions of olefins using ultraviolet photoexcitation of polyhalomethanes in the solution phase. We briefly discuss the possibility that the photochemistry and chemistry of the iso-polyhalomethanes may give significant release of reactive halogens to the atmosphere. (C) 2000 American Institute of Physics. [S0021- 9606(00)00148-3].