SCATTERED-LIGHT AND ACCURACY OF THE CROSS-SECTION MEASUREMENTS OF WEAK ABSORPTIONS - GAS AND LIQUID-PHASE UV ABSORPTION CROSS-SECTIONS OF CH3CFCL2

Ultraviolet absorption cross sections of CHCFCl2 (HCFC-14lb) were dete rmined in the gas phase (190-260 nm) and liquid phase (230-260 mm) at 298 K. The liquid phase absorption cross sections were then converted into accurate gas phase values using a previously described procedure. It has been demonstrated that scattered light from the shorter-wavele ngth region (as little as several parts per thousand) can seriously co mpromise the absorption cross-section measurement, particularly at lon ger wavelengths where cross sections are low. and can be a source of d iscrepancies in the cross sections of weakly absorbing halocarbons rep orted in the literature. A modeling procedure was developed to assess the effect of scattered light on the measured absorption cross section in our experiments, thereby permitting appropriate corrections to be made on the experimental values. Modeled and experimental regules were found to be in good agreement. Experimental results from this study w ere compared with other available determinations and provide accurate input for calculating the atmospheric lifetime of HCFC-14lb.