Photofragmentation dynamics of hydrogen peroxide: Analysis of two simultaneously excited states

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Abstract
The dynamics of the photodissociation of hydrogen peroxide has been analyzed by a complete characterization of the scalar and vectorial properties of the OH fragment using Doppler and polarization spectroscopy. When hydrogen peroxide is optically excited at 193 nm the hydroxyl radicals are formed exclusively in the X 2Π3/2,1/2 ground state with 84% of the available energy (Eav=417 kJ/mol) being released as OH recoil translation. The remaining energy is transferred in product rotation showing a strongly inverted rotational state distribution peaking at N‘=12. Vector correlations between the transition dipole moment of the parent H2O2 and the OH product rotational and translational motions were observed by Doppler broadened spectral lines and evaluated in terms of four bipolar moments. The quantitative contribution of two different electronic excited states in the dissociation process could be determined by analyzing the vector properties of the fragment. 62% of the OH products evolve from the à 1A electronic excited state while 38% of the fragments are formed via the B̃ 1B state when hydrogen peroxide is excited at 193 nm. The OH rotational state distributions when produced from the à 1A and the B̃ 1B state show no remarkable difference. The vector correlation of the recoil velocity vOH and the rotation JOH is strongly positive and increases with increasing JOH indicating a strong preference towards vOH and JOH being parallel to one another. The major part of product rotation is caused by a strong dependence on the torsion angle of the two upper potential surfaces.