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

Photothermal beam deflection (PTBD) spectroscopy using a free-electron laser (FEL) as a coherent pulsed pump source was applied for recording infrared spectra of actinide molecule complexes. We demonstrate that reliable spectra of samples containing uranyl and neptunyl compounds can be obtained in the mid-infrared region which was verified by conventional FT-IR spectroscopy. Since photothermal techniques are generally capable of detecting very low absorptions we tried to evaluate the minimum content of actinide ions which can still be detected by our setup of the PTBD 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 FEL-laboratory which is suitable for spectroscopic investigations in actinide research.