Governments and environmental agencies agree that fresh water is a scarcer resource. On the other hand, the world-wide implementation of intensive agriculture has led to an exponential increase in the variety and quantities of agrochemicals in natural waters, most of which are somehow resistant to degradation. Consequently, it has been claimed the need of ecoefficient water treatment methods to achieve a sustainable society.

Many different techniques have been attempted with questionable success to promote the degradation of these persistent organic pollutants. One of the most efficient alternatives to natural degradation of pollutants involves the use of UV/Vis radiation.

In this context, we present a study of the first stages of the photodegradation of sym-triazine-based herbicides. Geometries of neutral species are known, but this is not the case for the radical charged species that are short-lived intermediates in oxidative or reductive processes of these compounds. Laser flash photolysis and pulse radiolysis studies evidenced the participation of short-lived radical cations and anions in the mechanism.

Spectroscopic features of the radical cation and radical anion derived from sym-triazines are given. Red-ox potentials and pKa values of these short-lived species have been measured. Rate constants for reaction of sym-triazines with several radicals were used to establish linear free energy correlations.

The complementary computational study was done by using DFT at the B3LYP/6-31++G** computing level. The optimised structures of the radical cation and radical anion derived from sym-triazine undergo respectively an in-plane and out-of-plane Jahn-Teller distortion due to the presence of doubly degenerate HOMOs and LUMOs. Red-ox potentials and pKa values have been also calculated.

Acknowledgements. This work was funded by the Xunta de Galicia (Spain), project code: PGIDIT05TAM10301PR. We are indebted to the Centro de Supercomputación de Galicia (CESGA) for computer capabilities.

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