Uv-visible absorption cross sections of gaseous Br2O and HOBr

Abstract. The •bsorption cross-section of g•seous HOBr w•s determined over the w•velength r•nge 235 to 430 nm with • spectrM resolution of 0.6 nm full width •t hMf m•ximum (FWHM) using • diode •rr•y spectrometer. The spectrum of HOBr shows two mMn •bsorption b•nds with m•xim • near 282 nm (cr=(3.1:1:0.4)x10-•9 cm 2 molecule- • •nd 350 nm (cr=12.5 + 1.6)x10-2ø cm 2 molecule-•) extending out to 430 nm. The •bsorption cross-sections in the first •bsorption b•nd •re in good agreement with • recent determination; the cross-sections in the second band however, •re •pproxim•tely • f•ctor of 2.5 l•rger th•n previously determined. In •ddition we provide evidence in support of • we•k b•nd in HOBr •round 440 nm (cr•7.Sx10-2 • cm 2 molecule-•) •s observed by Barnes et al. [1996]. The •bsorption cross-section of Br20, which w•s used to prepare HOBr, w•s determined over the w•velength r•nge 230 to 750 nm. The spectrum shows four absorption b•nds with m•xim • •t 314 nm (or=(2.1 4- 0 3)x10-15 cm • molecule-l), 350 nm (cr=(•li • 4- 0.2)x10-• $ cm • molecule-•), 52 nm (cr--(4.4 4-0.5)x10-•0 m • molecule- and 665 nm (cr-(6.2 + 0.9)x10-•ø cm • molecule-•). The visible bands •t 520 nm •nd 660 nm h•ve not been observed previously. The equilibrium constant, for •h