IR SPECTROSCOPY WITH FELIX .1. PHOSPHORESCENCE DETECTION OF IR TRANSITIONS

The potential of the free-electron laser FELIX as a tool for IR spectr oscopy has been studied. Tuning the laser by varying the undulator gap has enabled the recording of spectra between 500 and 2000 cm(-1) in a single scan. It is demonstrated that IR absorptions can be detected a s FELIX-induced transient changes in the intensity of the phosphoresce nce from the lowest triplet state of a probe molecule. Using pyrimidin e as a probe in polyethylene, n-hexane and dodecane, IR transitions in the electronic ground state and the lowest triplet state of pyrimidin e have been observed. However, most of the intensity in the spectra de rives from the host matrix. Detailed IR spectra of n-hexane and dodeca ne have been obtained at liquid-helium temperature. These show a large number of previously unobserved combination bands.