UV VISIBLE AND IR ABSORPTION CROSS-SECTIONS OF BRONO2

The absorption cross sections of BrONO2 between 200 and 500 nm were me asured over the temperature range 298 to 220 K using a diode array spe ctrometer. The BrONO2 absorption cross sections are weakly dependent o n temperature at wavelengths < 450 nm (less than 10% change between 29 8 and 220 K) but decrease rapidly with decreasing temperature at wavel engths > 450 nm; at 480 nm the cross section decreased by similar to 3 5% in going from 298 K to 220 K. Our room temperature absorption cross sections are in good agreement with the measurements of Spencer and R owland (1978) over the common wavelength range of the measurements, 20 0 to 390 nm. We show that wavelengths longer than 390 nm must be inclu ded in the calculation of the BrONO2 atmospheric photolysis rate. We a lso show that photolysis of BrONO2 could be a significant atmospheric loss process for odd oxygen (due to halogen chemistry) below about 25 km, The infrared absorption cross sections for the BrONO2 band centere d at 803.3 cm(-1) were also measured. The integrated band strength was (2.7 +/- 0.5) x 10(-17) cm(2) molecule(-1) cm(-1).