Photodissociation of H2O2 at 193 and 222 nm: Products and quantum yields

Abstract

The primary quantum yields of OH(X 2Π),H(2S), and oxygen atoms [O(1D)+O(3P)] produced in the photodissociation of H2O2 at 193 and 222 nm have been measured at 298 K. At 193 nm, the primary quantum yields were observed to be 1.51±0.18, 0.16±0.04, and <0.02, for Φ(OH), Φ(H), and the sum of Φ(O) and Φ(O 1S), respectively. At 222 nm, the OH yield was Φ(OH)=2.02±0.35, the H atom yield was Φ(H)=0.024±0.012, and Φ(O) was <0.002. The errors quoted above are 2σ, precision plus estimated systematic errors. The OH product was directly monitored by pulsed laser-induced fluorescence, and the atomic species were detected via cw resonance fluorescence. The OH quantum yields reported here were measured relative to known product quantum yields in the dissocation of H2O2 at 248 nm. H(2S) yields were measured relative to those in photolysis of HBr and HCl, (at 193 nm) or CH3SH (at 222 nm), whereas O atoms yields were measured relative to O3 photolysis at both wavelengths. The present results indicate unit dissociation of H2O2 at both 222 and 193 nm with only two major products OH (∼80% at 193 nm, 98% at 222 nm) and H(2S) (∼20% at 193 nm, 2% at 222 nm). Up to 15% of the OH produced in the 193 nm photolysis may be vibrationally excited; however, no evidence for vibrationally excited OH was observed at 222 nm.