Photodissociation of H2O and D2O below 132 nm

A complete determination of the rotational and vibrational distributions in the OH/OD(A 2Σ+) fragments which result from the VUV photodissociation of H2O/D2O as a function of excitation energy is presented. VUV excitation was performed at eight different wavelengths (eleven for D2O) in the range between 132 and 124 nm. The vibrational branching ratios show a relatively fast rise of the vibrational excitation at threshold followed by a plateau. The general trend of the experimental results is well reproduced by a phase space theory calculation and by ab initio calculations reported by van Hemert and van Harrevelt. Rotational distributions seem to depend only on the available excess energy and, for a given excess energy appear to be similar for all vibrational levels in OH and OD.

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