The preferred values of the absorption cross-sections at 298 K are the values reported by

D. Maric, J.P. Burrows, R. Meller, and G.K. Moortgat, "Visible absorption spectra of molecular chlorine," J. Photochem. Photobiol. A: Chem. 70, 205-214 (1993); DOI: 10.1016/1010-6030(93)85045-A ,

who fitted the data for the wavelength region 250-550 nm with the following semi-empirical expression:

10²⁰ σ = α^0.5 × 27.3 exp {-99.0 α × [ln(329.5/λ)]²} + α^0.5 × 0.932 exp {-91.5 α × [ln(406.5/λ)]²}

where α = tanh (402.676/T).