ABSTRACT
In this chapter, the two main laser ionization spectroscopy methodologies, resonance-enhanced multiphoton ionization (REMPI) or resonance ionization spectroscopy, and zero electron kinetic energy (ZEKE) are covered. The chapter commences with a summary of fundamental aspects of REMPI, including an outline of the molecular selection rules and other factors governing its signal intensity, as well as a quantitative description of the REMPI process. Preferred experimental setups couple REMPI with time-of-flight mass spectrometry—REMPI-ToFMS; its “two-dimensional” nature (spectral and mass resolution) makes it an ideal tool for molecular spectroscopy, interaction processes, and analytical chemistry. The selected examples illustrate the versatility of REMPI. In fundamental research, it is used, e.g., in the measurement of dynamic “fingerprints” (the so-called state-resolved differential cross sections) of radicals and polyatomic molecules from uni- and bimolecular reactions, with rotational structure resolution. The examples for analytical chemistry applications include, among others, the measurement of isotopically resolved spectra in gas mixtures and the monitoring of volatile compounds (to unravel, e.g., biological processes); and in the discussion of polyaromatic hydrocarbons analysis, novel modalities with ultrahigh sensitivity are addressed (such as combining chromatography with laser ionization mass spectrometry). The focus of the final chapter sections is on ZEKE spectroscopy and the technique of H-atom Rydberg tagging. The description of the underlying physics and the unprecedented spectroscopic resolution is complemented by key examples, such as accessing the structure of molecular complexes (using ZEKE), or measuring individual partial-wave resolved resonance in atommdiatom reaction (using D-atom Rydberg tagging).
