Influence of H2O2 internal motion on scalar and vector properties of OH photofragments

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Abstract
The formation of ground state OH(X) radicals from the photolysis of jet cooled H2O2 at 193 nm is studied by Doppler and polarization spectroscopy. The features of the process are characterized by a complete analysis of the scalar and vector properties of the fragments. In the dissociation process 85% of the available energy is released into fragment translation. The remaining part emerges as rotational excitation that performs a narrow Gaussian‐like distribution peaking at N=12 with a FWHM of ΔN≂5. The vector correlations between the transition dipole moment μ of the H2O2 and recoil velocity v as well as angular momentum J of the products were evaluated in terms of four bipolar moments. The observed 〈μ ⋅ v〉 correlation was used to determine the state specific contribution of both the à 1A and B̃ 1B dissociative states to the overall product rotational distribution. On the average, 65% of the OH fragments are formed via the 1A state. A comparison of data obtained from the photolysis of room temperature and jet cooled H2O2 molecules indicates that transfer of parent rotation causes a symmetric broadening of the product distribution and a small increase in the 〈v ⋅ J〉 correlation [βvJ(T≂20 K)=0.5, βvJ(T=300 K)=0.7] of the fragments. In order to describe the influence of initial parent motion on the product state distribution and on vector correlations a model is used where the formation of two OH radicals in the same microscopic event is considered.