Reduced mechanism for the 366Â nm chlorine dioxide photodecomposition in N2-saturated aqueous solutions

A basic reaction scheme for the integral process of chlorine dioxide (OClO) photolysis at 366 nm in N2-saturated aqueous solution is proposed. The mechanism is supported by the initial quantum yield Φ°366 nm determined experimentally from OClO decay rates measured by electron spin resonance (ESR), chemical analysis of the stable products in solution and numerical simulation of the OClO profiles. In the concentration range 0.5 mM ≤ [OClO] ≤ 20 mM, Φ°366 nm = 0.52 with a 95% confidence interval of 0.50-0.55. Product concentrations determined after complete photobleaching were proportional to OClO initial concentration: [H+] = 0.856 [OClO]0; [HClO] = (0.141 ± 0.010) [OClO]0; [ClO3−]=(0.551±0.014) [OClO]0 and [Cl−] = (0.251 ± 0.015) [OClO]0. In the range of homogeneous light absorption, i.e. [OClO]0 ≤ 1.5 mM, OClO profiles and concentrations of the stable products in solution are well reproduced from numerical integration of the proposed mechanism. The reaction scheme requires the participation of dichlorine pentoxide (Cl2O5), which till now remains no isolated. However, reactions involving formation and hydrolysis of Cl2O5 are critical to reproduce the experimental profiles and explain the identity of the final products.