A dual wavelength range spectrometer system has been designed and constructed which can simultaneously perform single pass UV absorption spectroscopy and cavity enhanced absorption spectroscopy in the green region of the visible spectrum. Using the system the absorption spectrum of molecular chlorine has been measured, in the wavelength range 509–570 nm, using cavity enhanced absorption spectroscopy. Absolute absorption cross sections were obtained by simultaneous measurement of the UV spectrum to obtain the Cl₂ concentration. These are the first temperature dependent measurements of the Cl₂ absorption cross sections in this region which are vibronically resolved. Laboratory measurements were conducted at four temperatures (298, 273, 233, and 197 K). Spectral modelling of the Cl₂ B³Π(0_u⁺)–X¹Σ_g⁺ electronic transition has been performed, the results of which are in good agreement with our measured spectra.