Quantum dynamical studies for photodissociation of H₂O ₂ at 248 and 266 nm

A new quantum mechanical study on UV photodissociation of H ₂O₂ at 248 and 266 nm using a 2D fit to the Schinke-Staemmler's (SS) potential energy surface (PES) [Chem. Phys, Lett. 145, 486 (1988)] is reported. The rotational distributions of the product OH on both the à and B̃ surfaces are found to be considerably hotter than those obtained in a previous quantum study [J. Chem. Phys. 98, 6276 (1993)] using an empirical PES with a very weak dependence on the torsional angle φ. The new calculation shows that the rotation distributions in both the à and B̃ states, are Gaussianlike with a maximum at j=8 on the à surface and at j=9 on the B̃ surface at 248 nm. Similar distributions are found at 266 nm, but with the maximum shifting lower by approximately one quanta in both the à and B̃ states. The dissociation preferentially produces OH rotations with a high j₁∼j₂ correlation. These conclusions are in excellent agreement with the classical calculation of Schinke-Staemmler at 193 nm photolysis. Although the j distribution (rotation of OH) is similar on both surfaces, the J₁₂(j^→ ₁₂ = J^→₁ + J^→₂) distribution, which reflects the vector correlation of J^→ ₁ and j^→₂, is quite different on two surfaces. Our calculation shows that the à surface gives rise to more bending excitation than the B̃ surface, reflected by a hotter j ₁₂ distribution on the à surface. The à and B̃ state branching ratio of H₂O₂ is also evaluated at 248 and 266 nm photolysis.