Photodissociation dynamics of H2O2 at 248 nm. Photofragment quantum-state distributions and vector correlations

Abstract

Photodissociation of H₂O₂ at 248 nm produces vibrationally and rotationally cold OH(X²Π) fragments (ƒ_v < 3%, ƒ_R= 11%), the bulk of the energy release going into product translational excitation. The OH fragment translational anisotropy was studied by Doppler spectroscopy, identifying the dissociative state as a ¹A state. The translational anisotropy is high, β being close to its limiting value of –1, indicating a prompt dissociation. Doppler profiles were found to be sensitive to the polarisation of the probed transition and to the probe/photolysis geometry, indicating a correlation between J_OH and V_OH, fragment rotation being aligned along the recoil direction. Fragment rotation is predominantly generated by torsion about the O–O axis, either from breaking of the ν₄ torsional mode or due to a torsional dependence to the first excited ¹A potential.