UV characterization and photodegradation mechanism of the fungicide chlorothalonil in the presence and absence of oxygen.

An experimental and theoretical study of the UV spectrum of chlorothalonil (CT) was carried out and the vibrationally resolved HOMO→LUMO transition is presented for the first time. The fluorescence spectrum has also been recorded. Furthermore, preparative photolysis allowed a detailed study of the photoproducts formed with recognition of different isomers. In the presence of oxygen only the first reductive dechlorination-decyanation occurred, while in its absence a successive dechlorination-decyanation takes place.