Vacuum Ultraviolet Laser Spectroscopy of Small Molecules

Abstract

Publisher Summary This chapter presents a short coverage of various methods which have recently emerged with the advent of tunable coherent vacuum ultraviolet sources. Using lasers with sufficiently small pulse duration, time-of-flight spectrometers can also be particularly advantageous. In addition, high resolution, Doppler free spectra can be obtained using counter-propagating waves in which the ultimate resolution is limited by the homogeneous line-width of the atomic or molecular system. In order to overcome the problems associated with the AC Stark effect, it can, in some situations, delay the detection process after the end of the multi-photon excitation process. Because of the Stark-effect-induced changes of the spectrum, it is generally better for high-resolution applications to separate the nonlinear process from the atomic or molecular system to be investigated, and to expose the sample only to moderate VUV intensities. As an extension of the preceding wavelength selective technique, different overlapping electronic transitions can also be separated, exploiting the different lifetimes of the participating electronic states. This method is particularly valuable if the fluorescence of highly excited states is investigated where an excitation of lower electronic states cannot be avoided, because of subsequent cascade processes from the initially populated state which compete through their additional fluorescence.