Identification of actinide molecule complexes: A new vibrational spectroscopic approach at the free electron laser facility FELBE

The free electron laser (FEL) facility at the electron linear accelerator ELBE of the Forschungszentrum Rossendorf, Dresden, Germany, provides an optical laboratory which is suitable for spectroscopic investigations in actinide research. For the first time a great number of actinide elements which are currently in the focus of scientific work in the field of radioecology can now be investigated with laser spectroscopic techniques using infrared FEL radiation. The facility is also open for external users. In this work we present our first results of vibrational spectroscopic experiments for the identification of actinide molecule complexes by Photothermal Beam Deflection (PTBD) spectroscopy using an FEL as a coherent pulsed pump source which can be tuned throughout a broad wavelength range of interest. We demonstrate that reliable absorption spectra of test samples containing uranyl and neptunyl compounds can be obtained which was verified by conventional FT-IR spectroscopy. A prominent feature of photothermal techniques is the capability of detection of low absorptions. Therefore we tried to evaluate the minimum content of actinide ions which can still be detected by our setup of the vibrational PTBD spectroscopic experiment. It was found that the limit is obviously given by the background absorption of the hygroscopic KBr matrix of the samples which is originated by residual water. Furthermore, we present an overview about the technical equipment of the laboratory.