Mass selective infrared spectroscopy using a free electron laser

Mass selective gas-phase infrared spectroscopy using IR/VUV double resonance ionization is demonstrated. A free electron laser (FEL), tunable over the 100–2000 cm−1 range, is used as the IR excitation source while VUV light, produced by a F2 laser, is used for subsequent ionization. Spectra are obtained by monitoring the ion of interest as a function of IR wavelength. It is shown that these spectra can give the same information as direct IR absorption spectra. The sensitivity of the method is many orders of magnitude higher than that of conventional IR absorption spectroscopy. First results on para amino benzoic acid (PABA) are presented.