Degradation of polymers by oxygen reactive species formed from photoreactions of oxygen

Abstract

Being an endothermic allotrope of oxygen, ozone (O3) may serve as a precursor for reactive oxygen species such as atomic oxygen (\( {}^1{O_2} \)) and singlet oxygen (l02). The absorption of light by ozone consists of three bands: 200–320 nm (Hartley band), 300–360 nm (Huggins band) and 440–850 nm (Chappuis band) [352]. The primary photochemical processes differ considerably in each of these bands. The quantum yield of ozone photolysis at 254 nm is almost unity (\( \phi = 0.9\pm 0.2 \)). The main photoproducts are atomic oxygen (O) and singlet oxygen \( {}^1{O_2}({}^1{\Delta_g}) \), according to the reaction [704,990,1628]: $$ {O_3}\xrightarrow{{hv}}O({}^1D) + {}^1{O_2}(1{\Delta_g}) $$ (7.1) $$ O({}^1D) + {O_3} \to 2O + {O_2} $$ (7.2) $$ {}^1{O_2}({}^1{\Delta_g}) + {O_3} \to O + 2{O_2} $$ (7.3) The quantum yield of ozone decomposition at 334 is \( \phi = 4 \), indicating that one of the products must be excited species capable of decomposing O3 further. The primary process of O3 photolysis at 334 nm occurs according to the reactions [1628]: $$ {O_3}\xrightarrow{{hv}}O({}^3P) + {}^1{O_2}({}^1{\Delta_g}or{}^3\sum\nolimits_g^{ + } {} ) $$ (7.4) $$ O({}^3P) + {O_3} \to {O_2} + {O_2} $$ (7.5) $$ {}^1{O_2}({}^1{\Delta_g}or{}^3\sum\nolimits_g^{ + } {} ) + {O_3}\xrightarrow{{hv}}O({}^3P) + 2{O_2} $$ (7.6) From this mechanism, the overall quantum yield of O3 decomposition is \( \phi = 4 \).