Low concentration of toxic radioactive metals in environmental samples often
limits the interpretation of results of infrared studies investigating the
interaction processes between the metal ions and environmental compartments.
For the first time, we could show that photothermal infrared spectroscopy
performed with a pulsed free electron laser can provide reliable infrared
spectra throughout a distinct spectral range of interest. In this model
investigation, we provide vibrational absorption spectra of a rare earth
metal salt dissolved in a KBr matrix and a natural calcite sample obtained
by photothermal beam deflection (PTBD) technique and FT-IR spectroscopy,
respectively. General agreement was found between all spectra of the
different recording techniques. Spectral deviations were observed with
samples containing low concentration of the rare earth metal salt indicating
a lower detection limit of the photothermal method as compared to
conventional FT-IR spectroscopy.