The UV photolysis of Cl₂O₂ (dichlorine peroxide) is a key step in the catalytic destruction of polar stratospheric ozone. In this study, the gas-phase UV absorption spectrum of Cl₂O₂ was measured using diode array spectroscopy and absolute cross sections, σ, are reported for the wavelength range 200−420 nm. Pulsed laser photolysis of Cl₂O at 248 nm or Cl₂/Cl₂O mixtures at 351 nm at low temperature (200−228 K) and high pressure (∼700 Torr, He) was used to produce ClO radicals and subsequently Cl₂O₂ via the termolecular ClO self-reaction. The Cl₂O₂ spectrum was obtained from spectra recorded following the completion of the gas-phase ClO radical chemistry. The spectral analysis used observed isosbestic points at 271, 312.9, and 408.5 nm combined with reaction stoichiometry and chlorine mass balance to determine the Cl₂O₂ spectrum. The Cl₂O₂ UV absorption spectrum peaks at 244.5 nm with a cross section of 7.6_−0.5^+0.8 × 10⁻¹⁸ cm² molecule⁻¹ where the quoted error limits are 2σ and include estimated systematic errors. The Cl₂O₂ absorption cross sections obtained for wavelengths in the range 300−420 nm are in good agreement with the Cl₂O₂ spectrum reported previously by Burkholder et al. (J. Phys. Chem. A 1990, 94, 687) and significantly higher than the values reported by Pope et al. (J. Phys. Chem. A 2007, 111, 4322). A possible explanation for the discrepancy in the Cl₂O₂ cross section values with the Pope et al. study is discussed. Representative, atmospheric photolysis rate coefficients are calculated and a range of uncertainty estimated based on the determination of σ_Cl2O2(λ) in this work. Although improvements in our fundamental understanding of the photochemistry of Cl₂O₂ are still desired, this work indicates that major revisions in current atmospheric chemical mechanisms are not required to simulate observed polar ozone depletion.