IR SPECTROSCOPY ON GAS-PHASE MOLECULES WITH A FREE-ELECTRON LASER

Mass selective gas-phase infrared spectroscopy using pulsed, high powe r InfraRed (IR) radiation produced by the Free Electron Laser (FEL) 'F ree Electron Laser for Infrared eXperiments' (FELIX) is demonstrated. Two complementary excitation schemes are used. In the first experiment , para amino benzoic acid (PABA) is infrared excited using FELIX and t hen ionized using a vacuum ultraviolet (VUV) F-2 laser. In the second experiment, C-60 is multiphoton excited by FELIX to energies high enou gh that the molecule can undergo autoionization. In both experiments, spectra are obtained by monitoring the ion of interest as a function o f IR wavelength in the 100-2000 cm(-1) range. It is demonstrated that these spectra contain the same information as direct IR absorption spe ctra. The sensitivity of these methods, however, is many orders of mag nitude higher than that of conventional IR absorption spectroscopy. De tails of the two different ionization mechanisms are discussed. (C) 19 98 Elsevier Science B.V. All rights reserved.