Vacuum ultraviolet absorption spectra and photodissociative excitation of CHBr2Cl and CHBrCl2

Abstract

Photoabsorption and fluorescence excitation spectra of CHBr2Cl and CHBrCl2 trihalomethanes were measured in the 106–200 nm region using synchrotron radiation as a light source. Main photoabsorption bands observed are assigned as the Rydberg transitions of the outer shell orbitals. In the photoexcitation of CHBr2Cl a diffuse emission band of CHCl(Ã 1A″→X̃ 1A′) was observed in the 500–800 nm region. The radiative lifetime of the CHCl(Ã 1A″) state was first determined to be 7.01±0.25 μs. In the photolysis of CHBrCl2 at 121.6 nm, the formation of CHCl(Ã 1A″) and CCl2(Ã 1B1) radicals were observed. The fluorescence thresholds for CHBr2Cl and CHBrCl2 start at 162 and 159 nm with the maximum yields of 5% and 11% at 122 and 119 nm, respectively.