Primary photophysical and photochemical processes for cerium ammonium nitrate (CAN) in acetonitrile

Cerium ammonium nitrate (CAN) is an important photolytic source of NO₃^• radicals in aqueous nitric acid solutions and in acetonitrile. In this work we performed the study of primary photochemical processes for CAN in acetonitrile by means of ultrafast TA spectroscopy and quantum chemical calculations. Photoexcitation of CAN is followed by ultrafast (< 100 fs) intersystem crossing; the vibrationally cooled triplet state decays to pentacoordinated Ce(III) intermediate and NO₃^• radical with the characteristic time of ca. 40 ps. Quantum chemical (QM) calculations satisfactorily describe the UV-vis spectrum of the triplet state. An important feature of CAN photochemistry in CH₃CN is the partial stabilization of the radical complex (RC) [(NH₄)₂Ce^III(NO₃)₅…NO₃^•], which lifetime is ca. 2 μs. The possibility of the RC stabilization is supported by the QM calculations.